That's cute to think that way when the last couple of chapter have shown Eiko being gloomy and lightening up only when she hugs Kamu, it almost feel like it's the opposite.
Eiko loves Kamu in a platonic way, that's pretty clear with what you're saying, Kamu has never made Eiko's heart beat faster, in fact it's the opposite because when Sensei does anything to Eiko, she hugs Kamu to calm herself down, in short Kamu is the opposite of exciting for Eiko, she even wanted to dress her in a maid outfit this chapter because how cutely childish she'd look in it.
They're childhood friend. She doesn't need to do anything, they already have a special relationship on their own and Kamu have done more stuff with Eiko than Eiko with Sensei. Don't let the ship blind you.
Not only childhood friends never win, but they only were together for a few days in their childhood and Eiko left a way bigger impact on Kamu than Kamu did on her, that's the point of the flashback like a dozen of chapters ago. Plot twist, Sensei also was on Eiko's past according to chapter 78.