Toko Fukawa was a siren, though she was never really wanted or liked by even her own kind, she was always mocked and bullied. In turn, she developed an alter, Genocide Jack, who would hunt other sirens for sport. She often spent her days making up stories in her head, writing them down onto seagrass or telling them to anyone willing to listen.

Despite the fact that sirens were recently discovered by humans and are being actively tracked down, Toko continued to follow ships that leave the coast and altered to Genocide Jack to hunt the male humans attracted to her siren song.

Komaru Naegi was a human who was currently on a yacht owned by the Togami Corporation at midnight. As far as Komaru knew, her brother, Makoto Naegi, was invited by Byakuya Togami for a reason unknown to her and she was also able to come along, Komaru accepted, she thought that it’d be fun.

Unbeknownst to Komaru, she didn’t do well on ships, she felt nauseous and like she was suffocating in her room. Komaru clumsily stumbled to the outside area of the yacht for some fresh air and leant against the railings for support, however, she heard a faint singing far out into the ocean, a siren song. In a moment of poor coordination and distraction, Komaru fell overboard and plummeted into the raging waters below.

“Mwahahaha! I bet you're regretting this now, human!” Toko laughed maniacally and gleefully through Genocide Jack, her eyes locked onto Komaru as she tried to reach her through crashing waves.