ok so now there's a part 3 of this, and from what I understand thanks to DeepL, it's clear that part 3 happened after part 1 and 2 and it's from Kanon's pov. In part 3, Kanon was questioning her friendship with Chisato, which means that Kanon and Chisato was not dating from the start.
"かのちぃ前提のれんちさ"
The description says the setting of this is that Kanon and Chisato are already together but then leading from that into the Ren x Chisato pairing.
I think you're wrong about this. It's more likely that the author means "KanoChii story with RenChisa at the start".
At part 3, the author even wrote "かのんちゃん視点です" which roughly translated to "It's almost KanoChii now".
Anw, with that I believe that the cheating tag is wrong and should be removed.
Also, here's the link to part 3, just in case anyone ask: https://www.pixiv.net/en/artworks/93936545