First off, while going to Megumu's school, Mitsuru actually does end up meeting Aoi's half sister, Shino. In fact, they become really fast friends. (And a bit more that I won't spoil). Anyway, Mitsuru ends up helping her out with some bullies, but not knowing she was deaf, ending up being a bit inconsiderate. Shino can sign and lip read, but she can't talk. So he was kind of like: "Why don't you just say no to them? Stand up for yourself?" and stuff like that. Not realizing that the reason she didn't was because she couldn't. Once he learns this, he actually learning sign language, first to apologize, but then they actually become friends, so he wants to communicate with her better. Since he's disguised as his sister, Megumu decides that she should learn it to, to keep the crossdressing for a week thing a secret. Leading to THIS adorable scene.

Okay... I love this. I love that sign language became a way for these twins to start bonding and really talking to each other once again like when they were kids. They weren't on bad terms or anything, they just... grew distant as they grew up.

Now here's where all of this becomes important. Since Shino is Aoi's sister he ALSO knows sign. (BTW the sign in this manga is JSL. Just getting this out of the way now). Remember how Aoi can't get close to women? This leads into one of the most adorable love confession scenes I think I will EVER see.

So context: Megumu (nickname: Mego) was standing on a bridge. They couldn't hear each other because of the traffic. So... instead of using words...

She used sign (dies inside). This scene is also just hilarious. She keeps thinking she's signing wrong and this poor dude is getting so flustered. Oh my god I CAN'T with this manga.