Jii-san Baa-san Wakagaeru

The story is about Ine and Shouzou, two pensioners well into their 80s who are mysteriously returned to their 20s one night. Note: Sixth place of Tsugimanga 2020 Award in the Web Manga Category

Jiisan Baasan Wakagaeru is a web manga released on the author's pixiv and Twitter accounts, and later picked for print release by Kadokawa.
Includes 4 extra chapters