Nahoshi Inami, known as the Gravedigger, is a central antagonist and serial killer who manipulated her boyfriend Haruka Kazuta into committing murders for her pleasure. She derived enjoyment from watching victims suffer during their deaths, livestreaming the events online. Kazuta buried victims alive in fermentation capsules with minimal movement space, providing air canisters to prolong their agony. The livestreams continued after death to display decomposition. Their victims included Ayase Minami, Kouda Shiki, Yamashita Toshiki, Shiina Kaori, Masuda Kazuyuki, and Mishima Kana.

Significant childhood trauma shaped Inami; at age 14, she witnessed her mother's suicide by train while onboard the same carriage. Her name incorporates the kanji for "seven" and "star."

Following the Gravedigger case, Inami was captured but fell comatose. She was later repurposed as a last-minute Mizuhanome system operator to investigate the id well of Mana Tsurumi, leading to her digital persona manifesting as the Brilliant Detective Hakaido.

Inami possesses dark brown hair often swept with bangs to the right, light brown or golden eyes, and typically wears a pink sweater with a necklace. Her relationship with Kazuta extended beyond criminal activities, as promotional materials depicted them together in various contexts, including rebroadcast announcements for specific episodes.