Yobidashi! Subject ~Osananajimi Ane ga Hoken'i~

Big Sister Seika is Minoru's classmate and his childhood friend -- they've been together ever since they were young.

Hijiri, being unable to decide on a profession upon university graduation, is a jobless university graduate who one day, by some mistake, came to Minoru's school as a public doctor.

When he goes to check out the health room, he's pushed onto the bed and tied down!

After that, he's called out by her through text messages to his cellphone to repeat their secret affair...what are Seika's -real- intentions?

[From dlsite]