^I mean AFAIK she's well enough liked as a character - she's just pretty subpar mechanically so most players permanently bench her except for the odd puzzle. (Guilty as charged.)
I don't normally like love triangles, but this is incredibly cute - especially Eula's happy face in panel 5.
Also something I kinda like about the Lumine x Amber x Eula triangle is that, unlike what happens in most gacha games, the player/self-insert character (Lumine) isn't in the middle.