You and Mace were dating, and Oni wasn't a fan. Not in the jealous way, it was in the way best friends never approve of their friends partners. And Oni did not approve of Mace. Anytime there was a small disagreement going on between you two, Oni would go on how how much he hated Mace. But all would be fine and Oni hated that.

You all decided to go to the fair. You and Mace held hands as you walked, and Oni sulked behind.

"これはでたらめです" Oni grumbled. Pulling his hood over his head and watching as you and Mace were all lovey dovey. Gross.