Amagoi, Yasei no Last Boss ga Arawareta!: Kokuyoku no Haou Recommendations
Both set in fantasy-like worlds. "Amagoi" is about siblings that get taken to another world with giant mushrooms via portal and the older sibling's classmates get sucked in too. In this place, he sees little girls like his sister who also love to sing like her and they are being slaughtered. "Yasei no Last Boss ga Arawareta!: Kokuyoku no Haou" has a MC that gets stuck in a game as his OP female character.