Wakasama no Dekiai, Okotowarishimasu!

Kotori Hatsuse is a high school teacher, an exemplary good one who always thinks of her students first. And her students also treat her like a friend. One day, Kotori gets tangled up with some hoodlums by accident, and is saved by a handsome young man. He is Soichiro Haibara, a former student of hers from four years ago, who beat up the hoodlums with his uncommon strength. After the unexpected reunion, they decide to go out for dinner. But then the thug and his friends show up again. "I'll always protect you, Sensei..." Kotori is surprised by Haibara's unexpected confession, but when he embraced her with his strong arms, she couldn't help but feel her heart pounding... (Source: Comic Donna, translated)