Takatsuki

Ryousuke's colleague and the administrator of Building B, Takatsuki is an arrogant man whose depravity enabled him to engage in acts of perversion involving Haruka. While Ikumi is imprisoned he revealed to her the true nature of Shounen and how her mind and body is being slowly corroded.

Spoiler

Later on he was killed by Shounen when the boy was attempting to rescue Ikumi.