Ayako Sugiwara is the stage 4 boss of Chuhou Joutai and is Driller’s ex-girlfriend. If you ever play Chuhou Joutai, you can obviously tell about her ordering Driller to rejoin the Secret Sealing Club (abbreviated as SSC to avoid trademark conflicts). You can obviously assume that Driller is a former member of the Secret Sealing Club.
But who are even the Secret Sealing Club anyway? The Secret Sealing Club is a student group based in Kyoto, Japan that investigate the existence of Kozan, as well as its underground realm the Netherworld and even the Moon. They also research the time when Japan during the Edo period did not recognize the country of Kozan. Ever since the group was founded at Kyoto University, the group expanded into Kozan mainly through internet presence.
It is implied that Susumu Takajima and Ayako Sugiwara are members of the SSC. They appeared to be members of their Bonfire (the in-game version of Discord) server in the early 2000s. Driller left in early 2004 shortly after graduating junior high school. Even though the SSC is a college club, some of their members are aged 13 – 18 years of age.
Driller had known Ayako since fourth grade. What contributed to their break-up was conflicts during their eighth grade year. It wasn’t until Driller developed chunibyo (eighth grader syndrome) and revealed to Ayako that he has the power of what the Kozanese Royal Defense Force (Kozan’s military) specializes in. Driller also got obsessed with the music of Kagami Ochiai, which Driller later recruited into the Kozanese Royal Defense Force after they graduated.
The break-up was finalized when Ayako attended a different high school than Driller. However, in her in-game description and the original trailer, Ayako appears to be friends with Kagami Ochiai (please no yuri pairings). Ayako also appears in some of Kagami Ochiai’s album art, usually dressed in an outfit that best defines the album’s theme.