He was the first King's Chair of the "Guardians" and their founder. Manages the planetarium as a part-time job. Artist of the artbook "Kokoro no Tamago" (The Heart's Egg). Looks similar to Tadase. At first, he is thought to hold the Humpty Lock. A cat lover and has a liking for Ikuto's cat ears. He plays as a minor character but seems to have a bigger role in the story, considering that it is he who assigns the Guardian Chairs and is often seen counseling Tadase.

Spoiler

Tsukasa is Tadase's maternal uncle.