デリヘル呼んだら君が来た (Deriheru Yondara Kimi ga Kita)

Background
No, let's not change those things. "Deriheru Yondara Kimi ga Kita" is about a boy who's trying to get over his ex by hiring a prostitute only to find that the prostitute he hires is his ex-girlfriend.

This song is the 32nd published work of Nanahoshi Kangengakudan, and also his most notable song, having entered Hall of Legend.

It is featured in two compilation albums EXIT TUNES PRESENTS Vocalospace feat. 初音ミク, and EXIT TUNES PRESENTS NUMBERS.

Trivia

 * The on-screen lyrics uses the Japanese wordplay of 39 being read as Sankyuu which alternatively, means "Thank you" if translated to English.
 * Deriheru is an abbreviation of "Deribarii herusu" (デリバリーヘルス, lit. Delivery Health) which is a form of prostitution in Japan