He made his debut as a cartoonist in 1987 when Weekly Manga Action began running his Darakuya Store Monogatari.

For a year beginning in 1995, Usui's Super Shufu Tsukimi-San comic strip ran in the magazine Manga Life.

Usui was a devotee of Jehovah's Witnesses who had a church facility constructed adjacent to his home in 1994.

He was known in the industry to read out the New Testament for a full 20 minutes at each meeting with his publisher and handing them out copies of the Bible as a gift.

On September 19, 2009, a body with clothes matching those described in the report filed by Usui's family was found at the bottom of a cliff at Mount Arafune in Gunma.