Giyu and sanemi weren't exactly on the best terms. As you can imagine, when put on a mission together they clashed. Giyus cold demeanor and blank expression ; the polar opposite of sanemis rash expressive demeanor.

They were fighting a upper rank and it was a tough fight, they'd leave with harsh injuries. As they fought the uppermoon, it passed by quickly before Giyu sliced her head off in one clean blow, however she managed to use her blood demon art to knock them back. Giyu felt backwards and was pushed into the floor. Sanemi was pushed forward and fell to his knees.

She began to laugh as her body disintegrated "I can feel how much you hate each other, have fun" she smirked before her face disappeared into ash.

Both in confusion turned and as their eyes locked shock washed over them. Their eyes widened as the realisation arrived. They'd switched bodies.