Man, having a sister in this manga is a hazard if you want to stay a guy. Whether it's an older or younger sister. Also, damn. Five new characters and arguably one of the cuter extras from earlier in the story (Minato) now totally stands out on his own as interesting, instead of just being one of the "two boys" I kept forgetting the names of.
Fun thing -- if you go back and watch the Onimai anime, you can find a part where Yuuta and Minato are drinking juice boxes together. If you look at Minato's, you'll realize it's actually bright pink strawberry milk, something insecure Japanese boys his age would be probably shy about drinking in public. (consuming sweet things is considered somewhat transgressive for guys in Japan, especially something like that)
The writing was already on the wall that Minato is coded gender-nonconforming and this chapter seems to be the delivery on what was mostly just implied before.