Void_of_outer_box
Just some ideas for future World: Re:zero---Honkai(II or III)--- DxD---Medaka Box---Anos Voldigoad world(Silver Sea)---Little Garden(Problem Children)---I am a spider, so what---Douluo(just to beat Tang san)--- Tensura---To Aru(maybe he will became a Magic God)---Koyabashi Dragon Maid(It's a everyday type world, maybe combine it with the main world)---Haruhi Suzumiya World---Magi(It's low key SCP's Narratives type World if you consider upper worlds decided the fate of those lower).