Momo x Yuki from IDOLISH7. The translation in the beginning of the book is wrong. At the beginning of the book the stage staff are speculating about the girl wanting to date Yuki and them being like “but he’ll get caught in the tabloids if he acts on it!” So Momo jumps in all “Yuki already is dating someone teehee ME OF COURSE.” Anyone who knows IDOLiSH7/Re:vale knows that this is their schtick–acting like a ~teehee married couple~ on stage to play up the fanservice. So Momo saying this can be taken as a joke + him shutting down them gossiping about Yuki, BUT in reality he’s not kidding–they’re actually fucking behind the scenes. And Momo wants everyone to know it–that Yuki is his.