The Tunnel to Summer, the Exit of Goodbyes: Ultramarine, Volume 2 (The Tunnel to Summer, the Exit of Goodbyes: Ultramarine #5-8)

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.