100 Days of Deception | Theory Roundup: Who Is Shin Tae-jin?

⚠️ Spoilers for episodes 1–6 of 100 Days of Deception and the episode 7 preview. Guesses are labeled in the text as my take, pure speculation, viewer theory or reported.

In episode 3, Ga-kyung asks Hideo, "Who is Shin Tae-jin?" She doesn't know, and neither does Hideo. When he went to the Jongno pawnshop himself and asked, all he got back was that the name meant nothing to anyone there.

There's something odd about this drama: so many people have two names. Sato, Hideo, Ga-kyung, all of them. But exactly one person is a name with no face. It's the name written on the slip of paper in the wallet Ga-kyung steals in episode 1: Shin Tae-jin, owner of a pawned item that, as far as we can tell, nobody has come to claim in 13 years.

So this week I read through the comments. Comments on the Gordon Insight videos plus the most popular videos on other channels, over 4,000 in all. There were some really inspired theories, and when I boiled them down, the suspects narrowed to four.

That leaves one question for today. Who is Shin Tae-jin? We'll go through the clues one by one, and at the end I'll put down the Gordon Insight odds table and a new set of picks.

One pawn ticket

Let's start by looking at this slip of paper again. It's a ticket from a pawnshop in Jongno. The date is Taishō 8, which is 1919, the year of the March 1st Movement. The drama is set in 1932, so that's 13 years ago.

© tvN “100 Days of Deception”

In episode 2, Ga-kyung finds it strange too. She casually brings up a 13-year-old item to the pawnshop owner, and he asks who on earth would do that. Then he points something out himself: something left for 13 years would have to be something "you can't keep at home in case it's found."

Why a pawnshop instead of home? That's clue number one.

Clue two is the name. Shin Tae-jin sounds Korean to anyone. Hideo's Joseon name, per the official character profile, is Kim Tae-woong, so the ticket isn't his.

Clue three is where it was hidden. In episode 4, the place Hideo takes the slip out of is a flower-patterned box that appears to have belonged to his mother. And it wasn't at the bottom of the box. It was tucked inside the red lining.

On top of that, every episode's opening shows one pawn ticket lying on an open box. Episodes 1 through 6, without a single miss. That's how important this slip of paper is.

1919, a Korean name, and his mother's box. Who fits all three? Before we get there, let's look at the drama's name games.

Two names

In this drama, a name is never just a name.

In episode 4, there's a scene where Hideo has Ga-kyung read a document. She's supposed to be bad with Chinese characters, yet she reads the name of the editing section chief, Ishikawa, without trouble. But there's one more Ishikawa in this drama: Sato's old surname. In episode 6, Philip explains the backstory. Ishikawa rose through his in-laws' backing all the way to Inspector General. He took his wife's family name, Sato, and his given name changed too. We'll come back to that in a moment.

And Ga-kyung? At the Government-General she's Keum Seo-hee. So-ran, who gave her that name, admits in episode 4 that Seo-hee was the name of her dead daughter. Then in episode 6, Hideo digs into that name. What's your real name, then? Ga-kyung's answer was Gae-ttong. Instead of her real name, Lee Ga-kyung, she offered the name her friends used to call her.

Then there's the interpreter Suzuki in episode 1. He's the English interpreter at the Government-General, and when a senior of the Gugukdan calls him Suzuki, he snaps back, "Have you forgotten my Joseon name already?" That Joseon name still hasn't come up as of the end of episode 6.

By now you can see it. In this drama, names are masks. Which means Shin Tae-jin could be someone's mask too. Let's go behind that mask, starting with suspect number one.

Suzuki's Joseon name

The first suspect came from the comments on the Gordon Insight video. A man with a Japanese name who stands with the independence fighters: is his Joseon name Shin Tae-jin? That's Suzuki, the interpreter.

From what So-ran says to Suzuki in episode 1, he's someone who has lived as a spy for many years. When it started isn't said. And he was also secretly leaking the Gugukdan's activities and results to the newspapers, anonymously.

Then in episode 2, Suzuki is shot and rushed to the hospital. In episode 3, we hear that Hideo, after visiting him, asked that Suzuki be looked after because he has no family. A man with no family. So the only people who'd know his Joseon name would be the Gugukdan seniors, more or less.

But this theory has a big hole. Why would Suzuki's pawn ticket end up in a box in a woman's belongings in the Sato house? The only thread connecting them is the spying. If the owner of that box was a spy too, they could have been on the same side. I'll get to that under suspect three. For now Suzuki stays as my dark horse.

Ishikawa Nobuyuki

The second suspect is this man: the Inspector General, Sato Shinichi.

Ridiculous, you say? He's the man who trusts Koreans least. In episode 2 he says right to Hideo's face that he doesn't trust Koreans.

But this theory started in the comments on the Gordon Insight video. At first it was a single line: "Sato = Shin." When I asked why, someone replied that there are real families like that. It's one family's story, so it isn't a rule, but it kept nagging at me.

Then I rewatched episode 6 and one thing jumped out. When Keum Seok-jung faces Sato for the first time in 13 years, the name he calls him is "Ishikawa Nobuyuki." Sato's original name. Not just the surname changed: the given name went from Nobuyuki to Shinichi.

Here's the thing, though. In Japanese, one kanji can be read two ways. The character 信, "to trust," is read as "nobu" in some names and as "shin" in others. The drama hasn't shown Sato's kanji yet, so from here on it's my take: he may have changed every part of his name but kept one character. And if you read that character with its Korean pronunciation, it's "shin."

There's also something in episode 3 where So-ran lays out Sato's background. The Inspector General came to Korea in his father's generation. That sounds like Sato grew up in Korea, which got him labeled an outsider among the Japanese, and he tried to overcome that limit. Back in episode 1, it was Sato who took one look at So-ran, who was posing as a Chinese wife, and pegged her as somehow Korean.

So is Sato Shin Tae-jin? We have to check the counter-evidence too. In 1919, Sato was in Kyeam-ri as an army officer under the name Ishikawa. In episode 5, Sato remembers that year as the year an American reported it abroad and it blew up. The officer who burned down a village, pawning something at a Jongno shop under a Korean name that same year? I can't picture it.

Still, the earlier question stays. Why was that ticket in Sato's house, in a box that seems to have been his wife's? The owner of that box is suspect three.

A single line of voice

Hideo's mother. Her face has never been shown. All we've heard is one line in episode 4, to her young son home from school: "Did you have a good day?"

© tvN “100 Days of Deception”

The night that line aired, a post went up in a community forum saying the voice sounded like the actress Song Ji-hyo. The next day an exclusive report said that Song Ji-hyo plays Hideo's missing adoptive mother. The production team only said to check it in the broadcast. The report has one more line: she is Sato's Korean wife, and she vanished after giving birth to a daughter. That daughter would be Hanako. And I doubt they'd cast Song Ji-hyo just to show her from behind. That's my take.

That mother left home while Hideo was still little. That night, when young Hideo asked his father whether it was true, what his father held out in answer was a gun muzzle. Then in episode 6, Sato says of Hideo's mother that a Korean woman will always betray you, that she had promised a lifetime and left.

He uses the word betrayal for a woman who left. She didn't just leave. She did something.

And here comes the most-liked theory in the comments on the Gordon Insight video. If she really walked out, she'd have run off with the carefully hidden pawn ticket, so it's strange that she didn't manage to take it. Sharp, isn't it? A slip she hid by tearing open the lining, and the person leaving just leaves it behind? That bothered me most too.

That's where the spy theory comes from. Hideo's mother was a spy on the Gugukdan's side, who got caught while pulling information from beside Sato. That would explain the night with the gun. If she was a Korean spy, he'd suspect the Korean son left in the house too. In this theory, Shin Tae-jin is the name that mother used as a spy. Or the name of a man in her family.

But there's one more person in this house who remembers that mother: the housekeeper Yanagi. When Hideo asks for his mother's Joseon name, Yanagi says she doesn't know, then suddenly asks why he wants to know. When Hideo says he's looking for his mother, the camera lingers on Yanagi's face. A commenter on another channel noticed it too. Yanagi knows something. She's not a suspect. She's a witness.

So the question left is: who was Hideo's mother? Many people were looking for the answer in the same place. That's suspect four.

The half necklace

Episode 6, Ga-kyung's childhood flashback. A neighbor shouts in front of little Ga-kyung that her mother abandoned her daughter to live with a Japanese man. The gang boss in episode 3 said the same thing about Ga-kyung to Noma: a woman who had set up house with a Japanese man.

Yet the Ga-kyung of episode 6 remembers her mother like this: "My mom just found someone she loved more."

Now let's lay the two stories over each other. Hideo's mother is a Korean woman who pledged her life to a Japanese man. Ga-kyung's mother is a Korean woman who left her daughter to follow a Japanese man. One is the story of a daughter left behind, the other of a son left behind. They could be the front and back of one woman.

And there's an object connecting the two. In episode 6's flashback, a necklace hangs around little Ga-kyung's neck. And in episode 2, when the wounded Hideo bandages himself, there's a necklace on his neck too. Both are silver, and each is a half-moon shape cut straight on one side. The patterns on the outside look similar. Of course, whether they're halves of one necklace, we won't know until the two are held together.

© tvN “100 Days of Deception”

On the other channels, this theory by far had the most comments. Under the official tvN video, a comment asking whether Ga-kyung's mother is the adoptive mother Hideo is looking for got 399 likes. The Gordon Insight video had the identical theory. The necklace was split in two, and that mother was a spy.

So, back to the question from my Short: if this theory holds, are Ga-kyung and Hideo siblings? From what we've seen, they aren't siblings by blood. Episode 3 told us Hideo isn't Sato's biological son but a Korean adopted son who was an orphan on the streets of Gyeongseong. Even if both called the same woman mother, one was the mother who bore her and the other the mother who raised him. No shared blood. You can relax about their love line for now.

If it's the same mother, the three children are: Ga-kyung, the daughter she left; Hideo, the son she raised; and Hanako, her daughter with Sato. The blood line actually runs to Hanako, who would be Ga-kyung's half-sister with a different father.

The objections are serious too. A comment on another channel hit the bullseye. How does someone who abandoned her own daughter suddenly develop maternal feeling for a foster son and a new daughter? I think there's one answer to this objection. What if she didn't abandon her but couldn't take her along? A spy going into the enemy's house can't bring a daughter with her. That's pure speculation.

So is this mother Shin Tae-jin? There's one odd thing. Ga-kyung's surname is Lee. Lee Ga-kyung. But the name on the ticket is Shin Tae-jin. So where did the surname Shin come from? We'll return to that in the answer.

The comment detectives

A quick break. Here are a few more theories from the comments that made me slap my knee.

First, the housekeeper Yanagi. A comment on another channel reported that the character's name is Ryu Gwan-sil. Read the Korean surname Ryu (柳, "willow") the Japanese way and you get Yanagi. If the tip is right, a Korean surname is hidden inside a Japanese name. A device of reading one character in two languages, the same structure as Sato's Nobu and Shin. If the drama is really using this device, Sato's name can't be brushed aside either.

Second, the theory that So-ran is Shin Tae-jin. The comment's basis was the handwriting, but the date caught me more. It was 1919 that So-ran lost her daughter. And when So-ran points a gun at Sato in episode 1, the year she shouts is also "Gimi year, April" (Gimi is the traditional name for 1919). The date fits perfectly. Still, I can't yet see how So-ran's ticket would end up in a box in the Sato house.

Third, the theory that Sato is Ga-kyung's biological father. I'll push back on that one. The neighbor's insult was that she abandoned her daughter to follow a Japanese man. That doesn't mean Ga-kyung's father is that man.

Fourth, the theory that there's a Sato spy inside the Gugukdan. The point is that it's odd the operation in episode 4 leaked ahead of time. It's a separate matter from Shin Tae-jin, but it's worth watching in episode 7.

Taishō 8

Now let's line things up by date. In this drama, 1919 is not just a number.

The year turns up in what Ga-kyung throws at Noma in episode 1 too. Noma's parents died in the Gimi year, shouting for independence. For So-ran that year is when she lost the daughter she had after ten years of marriage. And that year, someone pawns something in Jongno under the name Shin Tae-jin. The very next year, Taishō 9, Sato leaves Korea for Japan, the year Fukuda confirms in episode 3.

Also, in episode 1, Sato introduces his daughter to Philip. "I have a 12-year-old girl." Twelve in 1932 means Hanako was born around 1920. And in episode 4, Hanako said her mother was Korean.

Lined up, it goes like this.

• 1919 (Taishō 8): "Shin Tae-jin" at the Jongno pawnshop. Kyeam-ri the same year.
• Around 1920: Sato leaves for Japan, and Hanako is born to a Korean mother.
• 1932: Hideo begins looking for his mother in Gyeongseong.

Going by the year Hanako was born, Shin Tae-jin is a name left behind around the time there would have been a Korean woman at Sato's side.

There are gaps, though. When exactly Ga-kyung's mother left hasn't been revealed yet. That's the biggest gap in this theory. And there's one more. In episode 1, Fukuda apologizes for missing the wife's funeral last year. Sato replies that surely no one could come from Gyeongseong all the way to Tokyo for such a thing. Whether that wife who died last year is the mother who left, or the Japanese wife from his in-laws, the drama hasn't said.

The Gordon Insight odds table

Now let me put down my answer. Four suspects, my odds table.

• Suspects 3 + 4 (Hideo's mother = Ga-kyung's mother): 55%
• Suspect 2, Sato: 20%
• Suspect 1, Suzuki: 15%
• Someone else: 10%

First place is the combination of suspects three and four: Hideo's mother and Ga-kyung's mother are one person. Three reasons. The story of a Korean woman who lived with a Japanese man appears on both sides in the same form, half a necklace appears on both sides, and the ticket was in that woman's box.

So who is Shin Tae-jin? I don't think it's the mother herself. Back to the question I set aside earlier: whether the "Lee" in Lee Ga-kyung is her father's surname or her mother's hasn't been shown. If it's the father's, Shin could be on the mother's side. If a woman in 1919 pawned something and wrote her father's or brother's name on the ticket, everything fits.

Today's answer

So here's today's answer. Shin Tae-jin is a name from the birth family of one woman who disappeared and left two children behind, maybe three. That's pure speculation.

A mother with no face, a Shin Tae-jin with only a name. The day her face appears, I think the name Shin Tae-jin gets solved too.

Gordon Insight picks

So here are three new picks.

1. Hideo's mother is Ga-kyung's mother.
2. That mother's surname is Shin.
3. Dark horse: if Sato's name in kanji is shown on screen, the same character that can be read "shin" appears in both Nobuyuki and Shinichi.

In the Hideo video, I only went as far as saying Shin Tae-jin is someone on the mother's side. Today I went one step further. I'll grade these right after episode 7 ends.

One last thing. The episode 7 preview has this question: "What happened back then?" The preview doesn't say who is asking whom. The answer might well include 1919.

What are your picks? 1 for Suzuki, 2 for Sato, 3 for Hideo's mother, 4 for Ga-kyung's mother. Leave your number in the comments on the YouTube video.

Sources

Reports and references

• Report on Song Ji-hyo's casting: SPOTV News (exclusive, Oct. 19, 2026), via Wikitree. Production team: "Please check it in the broadcast."
• Hideo's Joseon name "Kim Tae-woong": official character profiles, TenAsia and iMBC Entertainment (Oct. 10, 2026)
• Viewer comments: comments on the Gordon Insight video and on popular videos from other channels (over 4,000 as of Oct. 30, 2026). Only the content is quoted; no usernames.
• Episode 7 preview: official tvN DRAMA channel

The drama

• tvN 20th anniversary weekend drama 100 Days of Deception, episodes 1–6 (on Netflix and TVING, 16 episodes). Episode 7 airs Saturday, Oct. 31, 2026
• Starring Kim You-jung (Lee Ga-kyung), Park Jin-young (Sato Hideo), Kim Hyun-joo (Yoo So-ran), Lee Moo-saeng (Yoo Philip) and Jin Seon-kyu (Sato Shinichi)
• Directed by Yoo In-sik and Kim Yoon-jin · Written by Ryu Bo-ri · Produced by Studio Dragon and Romantic Crew

Images in the video and thumbnail

• The figure in a kimono (7:37 in the video, thumbnail): an AI-imagined image made with ChatGPT, not an actual scene from the drama. Face reference photo: K-POPIT / Wikimedia Commons (CC BY 3.0)
• Necklace comparison (video): scenes from episodes 2 and 6, enlarged and enhanced with AI upscaling (Upscayl)

The scene photos and dialogue in this post are quoted for criticism and review purposes; copyright belongs to their respective owners.