As Kusanagi and Kishitani walk to Yasuko's apartment, Kishitani remarks how Yasuko's neighborhood is ideal for single mothers, giving evidence of his bias in the case. Once their questioning is finished, Kishitani is confident that Yasuko had nothing to do with Togashi's death, having been moved by Yasuko's recounting of how she ahd Misato go sing Karaoke together. Kishitani is personally touched by Yusako's relationship with Misato and finds it hard to take her seriously as a suspect. This reinforces his role as a naive and amateurish detective who takes things at face value, becomes emotionally attached to suspects, and judges people based on superficial aspects of their life, such as Yasuko's being a single mother. Kusanagi, by contrast, while not as astute as Yukawa, feels intuitively that Yasuko's testimony is not quite right.

Even if he falls short of Yukawa in terms of deductive ability, Kusanagi is an astute observer and competent detective in his right. He notices the badminton raquet belonging to Misato while questioning Yusako. He notices the envelopes with the return address of Imperial University in Ishigami's mailbox while questioning. This is what will eventually enable him to connect Ishigami to Yukawa, which will go a long way in helping him unravel the case.

Kishitani teases Kusanagi saying, "You have a thing about the sciences don't you? Do I detect an inferiority complex?" which in turn brings to mind his relationship with Yukawa, who frequently teases Kusanagi for his errors in logic. This foreshadows the fact that he will eventually have to swallow his pride and turn to Yukawa for help.

Ishigami's logical abilities are reinforced by the math books strewn across his apartment, which fills Kusanagi with a sense of dread, as he was not particularly fond of math as a student. Throughout the chapter, Ishigami lives up to stereotype of a logic-minded math teacher, carefully planning out many details of how Yusako is to interact with the police and respond to their police. For example, he tells her to place the ticket stubs for her movie alibi in a pamplhet and not a draw so that it won't look too obvious that she is purposely storing the tickets to establish an alibi but also so that she will have enough evidence to support her alibi. The uncertainty about her alibi is by design on the part of Ishigami, as it raises just enough suspicion to keep the police focused on the issue of the alibi as opposed to other issues relevant to the case.

Despite Ishigami's knack for mathematical precision and logical consistency in anticipating the moves of the police, he also betrays his weakness, which consists of his feelings for Yusako. Even though it would be best for him not to visit the lunchbox shop, he still feels compelled to visit because he wants to retain a connection to Yusako and be able to see her. This is a fatal flaw in his plan, as it will involve him encountering Kudo, another man interested in Yusako, which will trigger feelings of jealousy in him. These feelings will be evident to others, namely Yukawa, who will be present at the lunchbox shop to take note of them. Ishigami's attachment to Yusako is such that he inwardly feels an emotional high upon hearing Yusako expressing gratitude toward him. While his yearnings for Yusako and his need for her validation are what motivate him to intervene in her affairs to begin with, they are also what will undermine his plans and lead to his the unravelling of his plans, which would otherwise have been strictly based on logic.

By failing to mention how he visits Yusako at the lunchbox shop, he has opened himself up to suspicion. Despite these error, Ishigami has planned for every possible eventuality. He is careful to avoid any contact with Yasuko and therefore only calls her by payphone in order to avoid leaving a record of his contact with Yusako by phone