I just had a facepalm "duh you moron" moment and figured out how to make Radiant Treasure Gun a LOT easier.
Iji-Donut: Ooh, Radiant Treasure Gun is so hard! The bullets twist and turn in such ways that it's impossible to consistently beat it in the corners! *cries moe tears*
Me: Hey Donut, you ever consider staying in the center?
Iji-Donut: Sniff...sniff...huh?
Me: Yeah, the bullets are much easier to dodge in the center, and you kill Syou at about the same time while upping your survival rate.
* Iji-Donut looks up and thinks for a moment
Iji-Donut: Eh heh heh... ;^_^
Cue me capturing Radiant Treasure Gun, Syou's second non-spell and Vajra in the same run.