10-nen-buri no Hatsu Kare ga Sugoi

Editor Hatsune is assigned a new role to a picture book author, "Ui-sensei," who turns out to be Mikado, her former middle school boyfriend! Hatsune's Mikado was her first love and first boyfriend. Now that she's reunited with him, she can't help but notice him...!? The two, who naturally drifted apart without even a kiss, are back together in this doting, redo-love story, doing everything they couldn't do 10 years ago!

(Source: Kodansha, translated)