Monitamon's head and color scheme are modeled after the Zaku II.
Daily Lives of a Lady: Yukana defending her not going to school: " Not even my father scolded me!".
His Japanese seiyuu Kenichi Suzumura has played Shin Asuka in multple works.
Episode 11: Yoshitake complains he's not Gundam.
These names are hints towards Okiya's actual identity, how Sera is Akai's sister, and that Amuro is The Rival to Akai. Masumi Sera and Tooru Amuro also have their names taken from there.
Case Closed: Akai Shuuichi and Okiya Subaru's names are references to Char Aznable from Mobile Suit Gundam, which Gosho Aoyama is a fan of.
The anime Arisu has Sebastian make, Arisuborg Alpha, is very clearly a reference to Mobile Suit Zeta Gundam.
In terms of actual ability, though, it's closer to the Sazabi.
Count Marylcian's Herschel looks incredibly similar to the Weltall-Id from Xenogears.
In Episode 10, the United Earth underground headquarters is clearly a reference to Jaburo, the Earth Federations underground headquarters in Mobile Suit Gundam.