Wasurenazuma no Kimi to

The manga's story begins in the modern day 21st century, with the elderly couple Towako and Kazuki. Kazuki loses his reason to live after her wife Towako passes away, having suffered from dementia in her final years. In despair, he tries to commit suicide by drowning with his wife's body. But he does not wake up to the afterlife, but instead to his second year high school days in 1966. With a second chance at a relationship with Towako, he will try to do it all over again.

(Source: ANN)