It's my head canon rin fucked archer everyday and night in order to constantly give him a supply of mana which is why he was able to use ubw twice without a master due to the high mama reserves he had as a result of sex with rin every night

It's my head canon rin fucked archer everyday and night in order to constantly give him a supply of mana which is why he was able to use ubw twice without a master due to the high mama reserves he had as a result of sex with rin every night