Caste Heaven Vol. 5 (manga)
It's the annual class trip, and Azusa is assigned to the same group as Atsumu and Kuze. While the three of them enjoy the sights in Kyoto, someone repeatedly attempts to harm Azusa. It isn't long before Karino, Azusa's knight in tarnished armor, comes to the rescue. The two spend the rest of the trip alone together, with their relationship undergoing a major change!