The Original CG and the VN depict him as faceless, but in the manga (both 18+ and all ages) and the OVA, he has a face.
A student with dwarfism and a strange disease that forces him to masturbate to remove semen from his body every 3 hours or else it will explode.
His special sperm(which is infertile) is a very valuable ingredients in the drugs that Dr. Amamiya produces. The disease is also why Yamada is very short, as past a certain point, his body produces sperm instead of the muscle needed to grow.
