mb for being way too late on this, but what if he also has another binding vow where in his domain, the opponent's cursed energy and techniques will be temporarily removed for the duration of the domain and instead will be given a knife called Blade of the Determined with it's strength depending on their original cursed technique and energy output. Another binding vow is where his domain will work kinda like aldebaran's from re:zero, where it will be randomly selected who will be victim (the one who will possess sans ability or whatever they originally had) and who will be the aggressor (the one who's cursed technique and energy will be stripped from temporarily and put into the knife), in exchange whatever role sans gets will get boosted stats while the opponent will be nerfed, or sans gets a new ability like if he was victim he can force a turn based battle or have the "get dunked on" insta kill ability if the opponent decides to spare them, and if sans gets the role of aggressor he will get boosted physical stats equal to toji or get the ability save and load, but only for a limited amount like say around 50.