This is a crossover between six Visual Art's/Key properties: Air (2005), Kanon (2006), Clannad (2007), Little Busters! (2012), Rewrite (2016) and Planetarian: The Reverie of a Little Planet (2016).
All the actors from the shows crossing over reprise their roles, with one notable exception: Asami Sanada voices Air (2005) protagonist Misuzu Kamio due to the character's original voice Tomoko Kawakami having passed away.
Kaginado is a portmanteau of the words "kagi" ("key", as in the studio Visual Arts/Key) and "nado" ("etc").