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Senku is all his life have been hiding he’s a half demon, the way people would discover about it, it’s the patterns on his skin but no one can see it cause his always using a lab coat or all the cloths for the boyband cover his body.
The only people that are on the known is the family that adopted him.
Byakuya and his family, they come from a prominent demon hunter family but he cut ties with his family when someone tried to kill toddler senku, because of the canon conversation about the moon byakuya worked for nasa for a while and later he retires as an astronaut.
He loves Senku with all his heart, that child right there is his son in all but blood, he would sacrifice the world for Senku but well (? on the other side Senku knows he’s love but sometimes he’s doubts about it; that’s one of his biggest insecurities (Trauma reaction).
Later when Byakuya gets married to Lilian, she’ll be on the known with her comes kohaku/ruri as stepsister, later suika as his baby sister. The way the introduce Lilian about senku been a half demon was a little hectic because they needed to explain the supernatural part. Koharu and Ruri find by accident a week before they were going to tell them.
Senku always wanted to reveal his secret to Taiju and Yuzuriha but he stops himself all the time, their reaction is something he doesn’t want to think about it and at the same time been a demon hunter.
Because of the incident when he was a child he doesn’t use martial arts or other techniques but he does it with science inventing stuff that kills the demons. Also apart from the incident even though he’s a half demon from his father side his human is weak, his mother had a weak body even byakuya was surprise she survive the pregnancy (well she still dies). He has a weak body but his stamina is good( demon perks) not always tho. When he lets his demon side out it’s different but again because of his insecurities about himself and he knows its stupid (but i want him to have a heavy trauma of the childhood memory that he was almost killed and thats were all his insecurity comes off ).
He becomes a really popular scientist around the time he is 16-17 with Chrome going on tv to explain stuff, because of his expressions and popularity Ryusui contacted him to form a boyband with chrome and him. Eventually they discover senku is a demon hunter cause there’s an accident where Ryusui and Chrome almost get killed.
They go to Byakuya so they can talk about been demon hunters, queue big bad comes to steal all the souls of the people so they use their songs plus demon hunters abilities to save the world.
When suddenly a new boyband appears (Gen/Tsukasa/Hyouga/Ukyou/Moos) and they are the demons using the entertainment industry not only as a boyband but other stuff like Gen as a mentalist.
Tsukasa, Mozu, and Hyouga as martial artist but for tv and Ukyo is just boyband. (? Well they capture souls and send them to feed big bad.
They met on the street when the demon group made his debut. Senku and co go to hunt them but failed, they follow the demon group but they are attack with a lot of demons because boyband B is trying to escape.
Senku follows Gen and he gets overwhelmed for something (? and part of his costume gets rip and Gen discovers Senku is a demon hunter and also he is a demon, the wall breaks senku panics covering the part that broke from his costume and Gen covers it and leaves.
Later Gen sends a spirit to ask senku to talk, Senku goes, they talk about Senku been a demon, Gen uses manipulation to know more it kinda works and at the same time it doesn’t.
When Senku leaves Gen is teleport to the big bad and he talks about his discovers and how Senku doesn’t hear the voices Gen and all other demons hear.
They have more encounters, talk about feelings in a twisted way.
Senku is having problems about hiding been a hunter and a demon at the same time, there’s tension. Like in the movie they need to won this big award cause when their song hits the right frequency the portal to the demon world closes, so with all this tension and secrets they tried to compose a great song but Senku keeps changing the lyrics.
Later Senku and Gen talk about Gen betraying big bad so he can be free. Gen gets transporter again to big bad and Gen tells them this was all part of his plan.
On the final concert for the awards everything goes well until demons attack Senku on stage looking like Ryusui and Chrome leaving all his mark expose, at the same time Ryusui and Chrome were running trying to follow some demons. When senku catch up with the real ryusui and chrome they feel betrayed about everything.
Big bad is winning and the demon boyband is making a big ass concert, to extract all the souls of the people. Chrome and Ryusui fall into a trance like the rest of the people that are going into the concert building.
(I haven’t decided if i kill byakuya or not the year before all of this) Cause senku ends up going to Byakuya family house, to see his technically grandmother and the person that almost kill him as a child. He has a whole break down and scream that he was just a child and didn’t know anything about his demon heritage yet. That was the incident were senku discovered the truth about it. His whole life he thought about that event on some way it end up as a trauma, that made him hate his demon side.
In front of his grandmother he has all his demon marks covering all his body and it’s bright. He ends up leaving while saying “I’ll use my demon side to end all of this”.
He goes to the concert his sings “What it sounds like.” (that fucking song make me cry and is one of the reason I decided to use senku as the half demon lol) Chrome and Ryusui are free from the trance, join him.
While they are singing the song, final boss appears, he is attacks sending demons but the trio quickly kills them. Then he attacks Senku and Senku use a shield but it doesn’t have enough power to protect himself.
From the side lines Gen is looking remembering everything they talk, how he feels about Senku. His last action is him protecting Senku, then sacrifice himself to save Senku while giving him two things. In conclusion they soulmates so hard that he gives his soul to senku.
Senku kills the final boss now using all his demon power, no end of the world but he suffers cause Gen is death.
Time skip Senku is researching science and is wearing a collar he got from a lady the first time he met Gen and Gen had it with him before his death, also his a little jealous about ryusui and ukyo having a happy ending (? (I feel lazy to write about their story so people can think of anything.)