A few stories were dedicated to Rina's attempts at proving that Meimi is St. Tail and Meimi trying to convince her of the opposite. How did that ended? Well, Rina had finally caught St.Tail and showed her face to Asuka Jr... Only to freak out when she touched St.Tail's manly moustache! Expecting to be caught, St.Tail had knocked out a burly and moustached male cop and dressed him with her costume and a wig for a last-minute swap, so she'd convince Rina that St.Tail was a male, and traumatized both her and Asuka Jr. in the process. She later explained what she had done to Asuka Jr. because she felt sorry for him, but Asuka Jr. went on saying Rina that St.Tail was a male...
Anime only: Asuka Jr. had been taken off the case and replaced with a special officer who used electronic trackers to chase Saint Tail. As Saint Tail is committing a heist, Rina is bugging her uncle the mayor to get Asuka Jr. back on the case, but the mayor replies that by then the special officer must have already caught Saint Tail... Cue the special officer breaking in the room, accusing Rina of being Saint Tail (cue hilarious WTF face) and starting throwing each other across the room, with the mayor and the officer's sidekick wondering what the hell is happening and Saint Tail's pet hedgehog (that had brought the tracker there) laughing its ass off. Needless to say, Asuka Jr. got back the case by the end of the episode.
The prequel manga chapter showing how Meimi first met Seira and Asuka Jr. and started going around as Saint Tail.
How Seira realized Meimi could help her recovering the stolen key of a confessional? Easy: Meimi couldn't resist the temptation to perform and summoned a kangaroo dressed with a tuxedo, and Seira (and the kid who would be peer-pressured into stealing the key) saw her.
Asuka Jr. had found out about the kid stealing the key because his friends would otherwise call him a coward for saying he had seen a kangaroo with a tuxedo. Asuka Jr. told him that doing something like that was the mark of a coward, and that kangaroos don't wear tuxedos... Cue him witnessing an horde of tuxedo-wearing kangaroos. Dancing.
When the still unnamed Saint Tail has left, having recovered the key, scared the kid into not doing it again and showed Asuka Jr. that stage magic is not mere tricks and scamming (previously Asuka Jr. had claimed this in class, and Meimi obviously took offence), the kid had marked her as a Phantom Thief, and Asuka was crying in despair because he couldn't understand what had just happened.
The day after, Seira shows Meimi the school journal with a bad picture of her (presumibly taken by Asuka Jr.) dubbing her a Phantom Thief, and, in an instance of Sure, Let's Go with That, told her she would go by Saint Tail and steal stolen things and give them back to their legitimate owners, and that she would pass her the information in the confessional whose key had been recovered by Meimi (Seira had kept it to 'reserve' the confessional for themselves). Seira is smiling all the time. Meimi is less than amused.
How did the chapter end? With Asuka Jr. reading about kangaroos to make sense of Saint Tail's trick while his father threatened to disown him if he tried to breed kangaroos.
In one occasion, Saint Tail wrote her 'burglary warning' on Asuka Jr.'s face while he slept. His reaction when he saw it in the mirror made it even funnier: first he freaked out, then... "I'm not washing my face".
As we are in the 'burglary warnings'... Once Asuka Jr. had been caught sleeping in class, and forced to read out loud from the book... And read out loud Saint Tail's message snuck in the book. After a few seconds of silence, Asuka Jr. realized what he had just read and freaked out.
Saint Tail's first warning: a balloon exposed right out of the school.