^Artists I think feel compelled to draw more happy times with these two. Maybe it's another world where they met under better circumstances, one where they get to live happily ever after together.
^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.