>>714133961
Because it has the same sort of Pink and Cheerful aesthetic that Hello Kitty does, while also handling subjects like death, loneliness, longing, and pain.
Also it's another show that they grew up watching, and there's something psychologically, empowering I guess? about reclaiming and reincorporating something structural to your childhood, as an adult.

There's definitely reason behind it, but as a guy that's just read some Jung, I'm way unqualified to write that essay. I'm just surprised less attach themselves to Goth Princess Hotaru.