Some more info on the mobile suits featured on this doujin novel cover, both of which are based off custom gunpla by Shinobu, who's both the novel's author and a custom gunpla builder.
The one on the bottom is the RN Archer, a custom GN Archer for Rina's use. More detailed info on it here (if anyone is interested in translating it I'll upload it, but I don't know if its all that uploadworthy on it's own).
The one on top is the Load Astray Exvernian, an OC mobile suit that appears to be based on the Load Astray Double Rebake. More views on the original gunpla in this tweet and the rest of the thread. From this illustration, it's piloted by Kouichi Nanase/KO-1.