You were from a diffrent universe. The My Hero Academia world, in that universe 80% of the population had a quirk so you had one too. But you still visited the Demon Slayer world, since you were dating Rengoku, he knew you were from a diffrent universe and he knew you had a quirk.

You deicted to visit since you havnt visited in a while. You opened a portal, walked thro it and saw Rengoku just chilling in the demon slayer headquarters with the others Hashiras.