Plot progressed to the point there Romio, Hasuki and Reon (The antagonistic character you saw in ch88) are contesting for the Black Doggies' (head) prefect position. On the other hand, Scott, Aby and Juliet are contesting for the White Cats' respectively. Reon is an illegitimate hafu and is basically a far left anti-unity extremist that wants to split the East and West starting with Dahlia. Don't blame her though, her family is so broken due to West isolationist ideology that she is legit tragic. Reon got the biggest dirt on Romio that is he's secret lovers with Juliet and so exposed them to gain votes off Romio to win the election. Reon sets up a scenario in ch86-87 which she knocks out the entire school's staff and sows discontent and starts a massive brawl between the two houses to make the reveal.
However, Maru is homo with Julio and the rest of the Black Dogs really like Julio, and White Cats are generally appreciative of Juliet. Rest is history as explained in the chapter.
tl;dr
Romio screwed up, his childhood friend Reon is an illegitimate hafu and a tragic antagonist. Reon is anti-peace and got the biggest dirt on Romio in the midst of prefect elections of which they were contesting.