“But I’m… just me,” is ripe for a callback. I hope we get something as on the nose as, “But you’re… just you.”
This chapter shows how the short length of this manga is used for impact. Several commenters have mentioned how authentic this feels. A lot of school life, mine at least, felt like short, violent stretches of emotion spaced out by hours sitting around wondering how someone feels, or what they think, or what they’re doing. Instead of four pages of teenage drama and sixteen pages of thinking about it, we get actual time.
Mitsuki’s self image issues feel very old school to me, too. She grew into a fascinating and charming person, but hasn’t had social encouragement from her peers to that effect. She’s sure she’s a goober, so if anyone sees her as desirable or interesting it must be those other people assessing her incorrectly. Tale as old as time, the only twist being the gender issues… which are also a tale as old as time, actually.
Mitsuki isn’t jealous, she thinks Aya likes a version of her that isn’t real, which means she’s worried Aya’s feelings aren’t real. We and Aya know Onii-san, the focused quiet person who works at the record shop, is real and just a part of Mitsuki. “But you’re… just you.”