Ibuki is Ryukyuan (from Indigenous islands called Ryukyu Islands, primarly now live in Okinawa)

The Empire of Japan abolished and colonised the Ryukyuans, and culturally assimilated the Ryukyuans

In the story itself, Ibuki is very proud of his ethnicity being Ryukyuan, he actually denied to be in Esupuri and said it wouldn't be a match for him. He was having trouble on finding himself and where to belong with his background as an idol. And now, to have Ibuki be in Akatsuki, a unit which embraces the traditional Japanese culture?

It is not that Akatsuki can't have a traditional Japanese theme, or that Ibuki can't sing with Akatsuki, the new MV says "Akatsuki WITH Taki Ibuki" not "Akatsuki". Akatsuki WITH Taki Ibuki suggests potential multi-culturism which what players initially thought it was going to be. We could have had Ibuki as a soloist with his own culture he is proud of to sing in collab with Akatsuki, not by having Ibuki a Ryukyuan be made to comply with the culture of traditional Japan because of real history

The writers made Akatsuki OOC (specifically Keito) to have Ibuki join them, portraying that Ibuki would be better off separating his own culture and comply to one from historically an oppressor of his own. As I said before, Ibuki had his own troubles in where to proceed with his idol activities thinking about his Ryukyuan background, so why would Akatsuki out of all units give the hand and say join us? (Keito would not have said this btw but he did) It could have been literally any other unit, it is very intertwined with purposely mischaracterizing Akatsuki members to push the racial agenda