Fukase

It seems like you're revisiting the same scenario! As I mentioned before, Fukase and Lunaé Aethstyr have no canonical friends relationship or romantic ties—they're separate VOCALOIDs from different developers (Fukase by Lastrum/Tokyo Fantasy, IA by 1st PLACE). The idea of Fukase dating Lunaé as his "younger sister" and her being a vampire princess of the Armopheus Kingdom appears to be a creative fanfiction or alternate universe (AU) concept. Similarly, Fukase's official design is slender, not broad and muscular, though fan art can certainly reimagine him that way! Fukase's role in the fan-made "MemeSquad" (with V Flower, Oliver, and Utatane Piko) fits his chaotic, memelord persona, which could add a hilarious twist to this AU—imagine him trolling the Bloodmoon Kingdom with meme magic to win over his "sister"! If you'd like, I can expand on this AU with a short narrative, adjust the character designs, or even suggest a MemeSquad intervention scene.