Kaguya, in Japanese mythology and folklore, is a legendary figure who falls in love with a mortal man. While the exact details of her story vary from source to source, the general narrative is that she appears from a bamboo plant and marries a man, though she must return to the heavens once a month.
The question of who Kaguya sleeps with seems to be left open to interpretation, as it is generally not explicitly stated in the original stories. Some interpretations suggest that Kaguya has a romantic relationship with the man she marries, while in other interpretations, she is content with being a platonic friend or spiritual adviser to him.
The overall context of Kaguya's story would suggest that a purely platonic relationship is the most likely interpretation, as she must return to the heavens once a month and is otherwise seen as an incapable of consummating her relationship. Ultimately, it is up to the reader to decide who Kaguya sleeps with and what their relationship is like.
