|S2 Episode 3 - My Little Sisters Are This Cute|
For no reason in particular, Maria comes over Kotaka's house and stays with him and Kobato. Kotaka calls Maria's sister Kate and she formally asks him to take care of Maria for the night. Maria and Kobato still hate each other, but they basically act like friends and spend the whole time playing video games together.
Then the 2nd half of the episode is all the characters hanging out in the party room at Sena's house and playing some sort of game where they pick random numbers and the number that's chosen has to do whatever is written on the piece of paper they pick up. At some point, Kotaka almost accidentally leaks out the secret that him and Yozora were childhood friends. Yozora objects when the game dictates Kotaka has to kiss Sena... so instead he does an indirect kiss by drinking out of Sena's cup. Sena obviously wanted to do it, but then thinks to herself and says "well, it wouldn't have meant anything if it were in-game anyway."
Later, at night some guy calls Kotaka and asks him if he's marrying Sena... wtf where did that come from?