Kotoko is guilty of at least one murder.
In a similar fashion of what happened in Apollo Justice: Ace Attorney Case 5: Turnabout Substitution. Tsumugu demonstrated that it is hard, but possible to climb up from the ground to the window on the 2nd floor (note that Fumi was killed on the 2nd floor and had her back turned to the window as she was strangled, possibly from behind), and Kotoko has climbed up a building from the outside in chapter 4 too. As for the motif, it is later known that the person who died at the 'drinking party' had a family name of Okino, and her brother has a contact name of 'Yu Okino'. If 'Okino' is really 'Masaru Okino', then he could be a lost sibling and thus, her motif may be Revenge, especially seeing that the first three victims were all members of the Black Club.
- Furthermore, before and during the Office investigation, she behaved very suspicious. Tsumugu asks her whether she's fine, and she says she's fine (with her sprite even jumping up) while a moment ago, you couldn't talk to her at all and when the topic swirls around Daimon, she says that if Sosei meets her, they have to solve another murder. During the investigation itself, she's standing in the corner covering the entrance to the underground warehouse so you cannot reach it during this initial investigation. Even before that, she had a 'surprise' ready, conveniently moments before Yuu was murdered.
- Confirmed! Even stronger, she is guilty of two murders.
