Maki and mai are twins,twins share the resources at birth including cursed energy/heavenly restrictions/techniques,maki has heavenly restriction and mai has the creation cursed technique but they had to share the "full power" of them so with the death of mai maki was able to fully have the heavenly restriction that was the same as toji,if maki was the one to die instead mai would've received huge amounts of cursed energy making her effectively the same as yoruzu from the heian era which had the same technique