Himitsu.

1. A Passing Story
A school doctor recounts a romance from her own school days.

2. Pink
A love triangle. It's set in the same school as "A Passing Story."

3. Romance
A couple from the same school as "A Passing Story" and "Pink."

4. Lover
Continues "A Passing Story" story in the present.

5. Himitsu. (Secret Love)
A girl deals with heartbreak.

6. Toiki (Sigh)
Shiratori, now in college, despairs of ever finding love.

(Source: Lililicious)