The Tunnel to Summer, the Exit of Goodbyes: Ultramarine (Manga) Vol. 2

Kaoru and Anzu have joined forces to study the mysterious Urashima Tunnel, which is rumored to give you your heart's desire--in exchange for years of your life. As they explore, connected by a length of string, the two students discover other connections in their everyday lives, including seeing a new side of Kawasaki, the school's arrogant queen bee.