Natsu e no Tunnel, Sayonara no Deguchi  

The Tunnel to Summer, the Exit of Goodbye, 夏へのトンネル、さよならの出口, Tunnel to Summer, Goodbye Exit, คำจากลาของคิมหันต์ ณ ปลายอุโมงค์, The Tunnel to Summer, the Exit of Goodbyes

The Urashima Tunnel has been the subject of a peculiar myth that claims those who enter will have their wishes granted but at the cost of their lifespan. Kaoru Touno initially dismissed this urban legend until he stumbled upon a mysterious tunnel one night. Despite his initial hesitation, Kaoru was tempted by the prospect of bringing back his deceased sister Karen, who had died in an accident five years prior due to his carelessness. As he ventured further into the tunnel, Kaoru discovered that its rules were not entirely clear, but he was determined to test its limits. Unbeknownst to him, his aloof classmate Anzu Hanashiro was also intrigued by the tunnel and decided to follow him on one of his expeditions. Although Kaoru was hesitant about her intentions, he eventually agreed to team up with Anzu in hopes of reviving his sister for the summer.

Natsu e no Tunnel, Sayonara no Deguchi won the Gagaga Award and Jury Special Award at the 13th Shogakukan Light Novel Award in 2018 under the title "Boku ga Urashima Tunnel wo Nukeru Toki" (僕がウラシマトンネルを抜ける時).It was published in English as The Tunnel to Summer, the Exit of Goodbyes by Seven Seas Entertainment under the Airship imprint on May 17, 2022.