Early on into their friendship, Sunny starts sleeping in Levi's room quite often. It originally happens as an accident like she falls asleep while watching anime/him game late at night, and Levi is too awkward to wake him up, but it soon becomes a normal habit between them.

Not in his bathtub (yes, Levi sleeps in a bathtub) because it's too small, and also, there's no reason for Sun to be in there at that point. But there will be a pile of like pillows and blankets in the area in front of his TV, and that's where he ends up sleeping fairly often.