|Relatives|| Tamago Yudin (father)|
Sankako Yudin (mother)
|Likes|| His family|
|Dislikes|| Being bored|
People messing with his friends
|English VA||Scott Menville|
|Japanese VA||Daichi Miura|
Like the past protagonists, , , , and , Kohaku's name contains the syllable "Yu", though it is in his last name instead of his first; a situation only shared with Jaden.
"Kohaku" means "amber". To Taylor Gorrell's knowledge, "Yudin" is not an actual Japanese word and thus has no meaning, chosen only to keep the "Yu" syllable.
Kohaku is described by people who know him as "complicated" and "complex". The main picture he shows is a fun-loving, somewhat nerdy, and good-hearted boy who enjoys Dueling. He greatly enjoys video games and is one of the biggest fans of the Game Cards used with D-Controllers, having collected over 30 different ones. A friendly guy, Kohaku is eager to please people when he can. As opposed to previous school-going protagonists and , Kohaku pays attention in classes and gets good grades, though he explicitly states he'd rather Duel than go to school. Kind and brave, but somewhat reckless, Kohaku will not hesitate to jump into the fray to help anyone in need. However, he is also blunt, sometimes without even realizing it, and has a tendency to not take people seriously when he feels he doesn't need to, acting nonchalant and sometimes cocky when someone is acting confrontational to him, making him seem rude at times, but when times call for him to be serious, he makes sure to give it his all. Kohaku uses honorifics when talking to most people, but according to him, any name he says with "-kun" and "-chan" is said to be a nickname, not to be respectful. He initially badmouthed Xyz Monsters, claiming they were old news, but after facing Cleo, he gained respect for them and has since dropped this facet of his personality.
Kohaku has two catchphrases: "It is ON!", said when he begins a Duel or is about to turn the tables, and "Duel Clear!", said whenever he wins.
As a running gag, Kohaku is extremely afraid of scorpions, resorting to even hiding behind his friends if he sees one. The only time this doesn't apply is to Plata's Buzzsaw Scorpion, due to seeing it a lot, but he is still nervous around it.
Kohaku is above average in strength for kids his age, and is also very smart.
Kinoko, Sokudo, and Hakaimo Yudin
Being their older brother, Kohaku loves all three of his siblings very much and helps take care of them, especially Hakaimo when she needs it. He is sometimes annoyed by Kinoko and Sokudo, but he can never hold it against them. It is revealed that Kohaku named all three of them.
Kohaku at first made a mental note to avoid Dizzy when he first meets him, but after talking with him in class, he sees the good person Dizzy is, and they become fast friends.
Kohaku met Jason when they were younger, and they have been friends for years and will have each other's back no matter what.
When Kohaku first met Plata, he was initially nervous around her, as not only was she the first girl he had as a friend, but her temper and destruction habit was very unnerving. Her use of Buzzsaw Scorpion also frightened Kohaku due to his fear of scorpions, but the two of them eventually managed to overcome these and become friends. At times it seems that Plata might have feelings for Kohaku, but eventually it becomes clear that she doesn't.
Kohaku has an interest in Nazoko, trying to get her to drop her loner persona, but it only serves to anger the girl. In the face of numerous warnings from Nazoko to leave her alone, Kohaku brushes them off and remains steadfast that he will get her to open up.
Aside from Dizzy, Yoru is the person who Kohaku has known the least, but they are still friendly nonetheless. Kohaku has a tendency to poke fun at Yoru's narcolepsy, but it's all in good fun.
- Kohaku Yudin's design is somewhat of an amalgam of design parts from various video game characters: Blonde hair with green top and headgear from The Legend of Zelda's Link, red shirt and red M-shaped fringe from Mario, blue back spikes from Sonic the Hedgehog, blue footwear from Mega Man, white gloves from either Mario or Sonic, and blue bottoms and green eyes from either Sonic or Mega Man.
- His habit of turning his visor backwards from a Duel stems from Ash Ketchum, the main protagonist of the Pokemon anime (further showing the video game basis), who had a habit of turning his hat backwards before battling a wild Pokemon.
- Kohaku's English voice actor, Scott Menville, is the same as Lloyd Irving from Tales of Symphonia.
- Kohaku's Japanese voice actor, Daichi Miura, is the singer of EXCITE and Life Is Beautiful, two songs associated with the partially video game-themed tokusatsu show Kamen Rider Ex-Aid.
- Kohaku is often associated with the number "589" (which can be read as "ko-ha-ku").
|Ren "Dizzy" Naginata||002-003||Win|
|Sykonetyk - Hydro||005||Win|
|Nazoko Ikari||007||Lose (w/ Yoru Mezameru and Ichika Konazuyo)|
Stemming from his love of video games, Kohaku plays a Pixel HERO Deck capable of powerful Composition Summons while using varied effects. He uses his Pixelated World Field Spells to give himself extra advantages. His wide variety of Game Cards makes it so no Duel with him is ever the same.