Hello Schoolgirl (2008)

They both involve a younger girl in love with an older guy who is reluctant to love her back.

Relationship between a older guy and younger girl.

Both involve a relationship between an older guy and younger girl.

Hello Schoolgirl was a little deeper. And it's not student - teacher, but the age gap is there. The schoolgirl and the older guy fall in love. It's fluffy cuteness (Kinkyori Renai was fluffier and cuter) and the ending was nice.

Following a failed confession to her first love, female high school student Mikoto Ochiai contemplates jumping off the roof of the school building. However, her thoughts are interrupted by the arrival of Jin Haiba, the physics teacher known for being a slacker and the butt of students' jokes. Calmly, he lights a cigarette and asks for an explanation of the events that led her to this precipice. Rather than dissuade her from killing herself, he makes a request—will she enter into a romance with him before she dies? Together, the two gradually ponder why they should keep living and why they should not love each other in earnest.

Relationship between an older guy and younger girl.

Both are about fortuity, chance meetings and other little things joining the main characters.

I think it was something between them and I love them!

They both are nice lovestories. Rather simple and quite serious with deep and reasonable feelings.
Calm and cute developement of feelings towards one another.