Books in the Yuuna and the Haunted Hot Springs series

When Yuuna''s talisman wears off, leaving her suddenly invisible in the middle of a performance at a music festival, the residents of Yuragi-sou have to think on their feet! Nothing they try seems to make Yuuna visible again. Meanwhile, what''s this about Yuuna and Kogarashi winning a night in a high-end hotel? At least she''s still visible to him...