Toujirou Mitake's ex-wife will turn out to be Vier Dreissig
Ryukishi 07 frequently writes callbacks to characters from his previous works.
Ciconia's "Toujirou Mitake" is a name callback to Higurashi's "Tomitake Jirou."
Ciconia's "Vier Dreissig" is a name and character design callback to Higurashi's "Takano Miyo."
Since Tomitake Jirou and Takano Miyo were lovers in Higurashi, then it is likely that their Ciconia-based counterparts could have been romantically involved.
In Ciconia, Toujirou Mitake mentions that his ex-wife left the affairs of the real world in order to retreat into her "hobbies." Could this be referring to Vier Dreissig's retreat beneath the Earth to conduct ominous research? Additionally, when Toujirou Mitake receives a reward from Jestress, all he asks in return is for her to remove her mask, which prompts him to remark that Jestress reminds him of when he first met his ex-wife. This may be another hint since Jestress resembles a younger version of Vier Dreissig.
