Sorry this took so long; Marisa's dialog in panel 2 seems, on the surface, to request that Yuuka NOT let her make Youka happy, but I finally figured there's an implied "ikenai" in there somewhere, turning the negative verb into a positive.
Yeah, this is one of those stories that I keep coming back to despite the "Soul Crushingly Depressing" portion. I have to read it all the way through, from beginning to end. And as Marisa stated, I feel like re-reading the portions where Youka was alive is re-experiencing the happy portions and would NEVER give them up to anyone. It warms me every time remembering how Youka was so cheerful and experiencing everything for the first time (her first Danmaku, her first Graze, her first prank on Cirno, etc...gods, just remembering those even having just read that puts yet another smile on my face) that I would NEVER allow anyone to give her painful memories. Exactly like Marisa.
Whether I'm miserable...It's okay.But in return......doesn't matter.I'll just cry it out over and over again....I'll never let anyone give her painful memories....You're a strong girl.