Keiki wakes up from a nightmare (in which he takes his new wife Sayuki out for a walk, like a dog) to find Mizuha in his bed, reiterating her love for him, kissing him, and essentially urging him to choose her among all his choices. Needless to say, she comes on too strong, and ends up pushing Keiki right out of the damn house.
He ignores Mizuha’s many calls and instead gets in touch with Shouma and Koharu, to tell him his situation and ask for a place to crash. Alas, Shouma’s house is full and he won’t allow Keiki to stay at Koharu’s. He also encounters Mao, fresh off a BL-writing all-nighter, who has bean cakes and milk at the ready for the hungry Keiki.
Mao only lends more evidence for her case as Best Girl by supporting Keiki without judging, while having her own thing going on separate from him. She may not be aware of Mizuha’s romantic love for him, and assumes they had a sibling spat, but she knows in the end the two of them will be fine. She even gets an accidental indirect kiss in!
The episode then widens into an extended montage with both Mizuha and Keiki attempting to text their feelings, but not actually sending any messages to each other. Keiki also called his dad, who confirmed that Mizuha was adopted, and Keiki warmly and immediately welcomed her into the family. It seems very odd he’d forget this.
In any case, even a single day away from home proves too much for Keiki, as he only just manages to get in the front door after getting caught in the rain before passing out, cold and feverish. Mizuha puts aside their present issue and takes care of her brother.
Mizuha calls Sayuki, who rushes to Keiki’s side and jumps in his bed to warm him. Sayuki also texts Yuika, reporting their boy is “defenseless,” but they ultimately can’t put their competition on hold long enough to calm down, so Mizuha kicks them both out so Keiki can get better in peace.
Keiki wakes up in the middle of the night, his condition improved, and once again walks in on a naked Mizuha in the bathroom. They stay on either side of the door trying to talk this thing out, and Mizuha mentions that her love for him began on that day when he welcomed her (which again, he forgot) and only grew from there. She lost her family in an accident, but gained a new one.
Still, Keiki had never viewed Mizuha as anything other than his little sister, and even though things will never quite be the same whether he accepts or rejects her love, he decides to remain that caring brother going forward. It’s a safe, sensible chocie that’s true to the character he’s been thus far.
That being said, he can’t weasel his way out of granting the command of the winner of the confession contest, and Mizuha wants him to be her boyfriend for a day. She concedes that going from brother to permanent boyfriend isn’t like flipping a switch, but seems determined to gradually change his mind.
It doesn’t help her case when he finds out her phone is full of selfies of her in various stages of undress. Turns out she’s a full-on exhibitionist! Looks like “normal” for Keiki was, is, and will always involve attracting women with particular tastes. A girl bereft of said tastes probably isn’t in the cards for him. Might as well go for Mao!