Natsu e no Tunnel, Sayonara no Deguchi: Gunjou  

Kaoru Tono came across a story about the Urashima Tunnel which is said to disregard the rules of space and time. It is stated that if you can find it and walk through it, you will discover your heart's desire on the other side, but in return, you must give up several years of your life. On this particular night, while standing in front of what appeared to be this mysterious tunnel, Kaoru was reminded of his sister Karen who he lost in an accident five years ago. Suddenly, Anzu Hanaki appeared, promising to assist him in exploring this enigmatic tunnel. However, what does Anzu want from Kaoru in exchange for her help? And after the tunnel has taken its toll on him, what will he have left to offer?

Natsu e no Tunnel, Sayonara no Deguchi: Gunjou was published in English as The Tunnel to Summer, the Exit of Goodbyes: Ultramarine by Seven Seas Entertainment from August 9, 2022 to June 13, 2023.