This is why, people, reading everyone's full name is important

I also realized, as I assumed Daiki took the surname name of his father (who i assumed was Takeru), but i reread ch 31 and it revealed Ueyama Mui. Although it is said that Daiki was raised by Ueyama Shinpei and Sho so Mui and Daiki must have been childhood friends. Also Daiki is Korean so that does make sense that he is not apart of the Ueyama Clan. So Daiki took over the clan after Mui died and Taichi wasn't a fan but grew to like him as a brother-in-law.

Daiki is a Ueyama, it was his father Takeru that married into the family, his mother was Reisa Ueyama the 9th head of the clan

wait i did not know this

Right I like I was reading something totally different from them

What

Also, it's Ueyama Reisa. She's japanese.

But if Miu wasn’t an Ueyama, then her surname name would be Joe or another name(her maiden name). It doesn’t make sense that Miu has the Ueyama name and Daiki doesn’t since she supposedly married into the family. It her surname is Ueyama, that would most likely be her maiden name since Asian women don’t typically change their names to their husbands and their children take on the husbands name.
Daiki is Korean not Japanese and he is like the 5th or something generation of ethically Korean ppl living in Japan in his family. Reisa was the 9th head, so if the Ueyama clan was ethically Korean, then he would be the 10th generation or something like that.
It makes the most sense to me that Daiki was adopted into the family and raised by them then married into the family. We don’t know Takeru’s last name so it’s definitely not confirmed but I have good suspicions that Daiki and Taichi are not blood brothers.

Wtf I'm more confused because of y'all's reply

Lol yes I know I wrote it that way cause I'm not Japanese and it was for easier understanding

Miu was a "a normal civilian" Taichi said so himself while telling Min about her my guess is she was added to the Ueyama family Registry, adopted into the family, thus changing her last name. Why Daiki uses the surname Joe I don't know, but also he seems to be Korean on his father so my guess is his paternal grandfather or great grandfather was Korean. They also stated that his mom Reisa had to fight to be the 9th head of the clan, so perhaps she had a brother that was meant to be head, we still don't have info on Taichi's parents so I'm not sure why Taichi was meant to be the 10th head of the clan or why he gave it up to Daichi

Alright I reread the last chapter and yea I fucking understand now, (correct me if I'm wrong) Daiki is Ueyama, he just took his father's surname. He felt that the only way for him to become part of that family is to become oyabun that's why he decided to be oyabun without changing his surname and the blonde dude is his brother. I'm fucking lost lmao

Season 1, chapter 15- Ueyama Shinpei, Daiki's grandpa confirms Toma is of his bloodline (Toma's great grandpa). In the same chapter, Taichi calls himself Toma's uncle, and he is introduced as Ueyama Taichi.
Season 1, chapter 17. -Taichi is said to be Daiki's younger brother
Season 1, chapter 18- Taichi tells Min Joon about Toma's mom, Mui, being a civilian, and that she was murdered by another gang
Season chapter 27- Min learns Daiki can understand some Korean, and Daiki confirms his name is Joe Daiki, he has a Korean surname. He says he's a 3rd generation (Zainichi, ethnicity Korean, nationality Japanese) making Daiki either half-Korean half-Japanese or a quarter Korean and 3 quarters Japanese (depending on his paternal grandmother)
Season 1, chapter 30- Sho tells Min about Daiki's parents, "His mother, Ueyama Reisa, beat all the male competition and became the 9th oyabun. Takeru-sama was a real man, as far as I could tell." Then talks about Reisa's death, but we don't find out what happened to Takeru.
Season 1, chapter 31- Daiki and Toma visit Mui's grave, and Daiki says that he feels he ruined her life and is doing the same thing again (not a direct confirmation, but it feels like he's talking about how both Mui and Min are/were civilians)
Season 1, chapter 61- Ueyama Shinpei confirms Ueyama is his daughter and Daiki is her son, Toma is her grandson
Side 1- mentioned that Taichi is 2 years younger than Daichi
T
Side 2- mention Daichi having a cousin named Ayako (she didn't like being from a Yakuza family)
Season 2, chapter 6- Daiki receives his father's will, and Grandpa Shinpei refers to him, Daiki's father, as Joe-san confirming Daiki uses his fathers surname I believe that after Daiki's mother, Reisa, died, his father left the Ueyama, distraught, and went back to Korea. He had a business in Korea that Daiki can inherit if he lives and manages it from Korean. So he seems to have died more recently. He probably left Daiki in the care of Grandpa because he was Reisa son and was to be the next head, and or Granpa Shinpei wouldn't let him take Daiki.

Ita doesn't matter. The character is japanese.

Lol relax it's not that serious