Kou-2 ni Time Leap Shita Ore ga, Touji suki Datta Sensei ni Kokutta Kekka

Seiji Sanada, a nearly 30-year-old corporate drone, woke up one morning to find that he'd been sent back in time to the spring of his sophomore year of high school. Seiji had long regretted graduating without confessing to his beloved world history teacher, Haruka Hiiragi. So this time, he decides to tell her his true feelings...and she's surprisingly okay with it?! The two of them began discretely dating and their life as a couple was bliss... but Hiiragi-sensei is a woman so sweet, she’ll spoil her man rotten! A super flirtatious and rosy school life begins!

(Source: Manga UP!)

Notes:
- Original serialization ran for 61 chapters with Chapters 29, 40, 55 and 56 split into multiple parts. In the volume releases, these were all combined, as well as Chapters 47 and 48 as Chapter 47. One Tokubetsu-hen (特別編) published on Manga UP! was not included in any of the volumes.
- Includes six extra chapters.