Subaru is a reference to two SNK characters. The first is Sakazaki Yuri, daughter of Sakazaki Takuma (the original Mr. Karate, final boss of Art of Fighting). Takuma wears a tengu mask and largely turned into a comic relief character in KoF. The second is Todo Kasumi, the heir to Todohryu Aikijitsu who spends most of her time in the games looking for her dad. Subaru shares Yuri's background and personality but Kasumi's style of fighting and clothes. The weird hitboxes thing is a reference to Yuru's condition in early KoF games. Her background story says that Takuma only taught her basic Kokugenryu Karate style (meaning she doesn't have Ryo's special moves), so the game devs accidentally made her basic moves OP to compensate. But she herself was never as OP as Subaru.
Rindou is also a reference to another two SNK characters. The first is Kasumi's rival Li Xiangfei (SNK's answer to Chun Li), the second is SNK's eternal idol Athena Asamiya. Super Rindou's background is a bit meta. Li Xiangfei is a Chun Li analog and Chun Li's fighting technique also used to be an assassin style, so Rindou's continuing to fight American super heroes etc references Chun Li's progression, but monsters and aliens also reference Athena's non-fighting games Athena (where she fights monsters) and Psycho Soldier (where she fights aliens). Rindou's OP moves are also references to Athena's cheat-astic psychic moves in the SNK games.
Rindou is also a reference to another two SNK characters. The first is Kasumi's rival Li Xiangfei (SNK's answer to Chun Li), the second is SNK's eternal idol Athena Asamiya. Super Rindou's background is a bit meta. Li Xiangfei is a Chun Li analog and Chun Li's fighting technique also used to be an assassin style, so Rindou's continuing to fight American super heroes etc references Chun Li's progression, but monsters and aliens also reference Athena's non-fighting games Athena (where she fights monsters) and Psycho Soldier (where she fights aliens). Rindou's OP moves are also references to Athena's cheat-astic psychic moves in the SNK games.