Sometimes the best romances in anime are between two eccentric characters, or happen in off-beat circumstances, whether they're silly or just plain out of this world. There tends to be a tone of sweetness to complement the strange in these instances, and the couple may be people with disparate life experiences and coping skills, or an odd creature who has fallen in love with a human.
Source：https://www.cbr.com/anime-quirky-romances-ranked/
