Saint Tail's 'warning notes' double as Love Letters asking Asuka jr. for a date, and are heartwarming just by this, but some are particularly egregious:
in episode 3, it was a note sneaked in Asuka jr.'s book, like a classmate asking him a date (in a way, it was);
in episode 5, it invited him to an amusement park whose main attraction is a clocktower said to bring luck to couples who watch its dolls together;
And they did. Saint Tail even thanked him for the date.
in episodes 7 and 41, it was in a lunchbox Saint Tail prepared just for him (the second one even has Meimi looking at him wondering if he'll like it while holding a cooking book);
The second one is even bigger because Asuka jr. is now dating Meimi, and this time is properly embarrassed for eating food prepared by who he believed to be another woman (not that he had a choice: his lunch had been swiped away).
the Saint Tail doll in episode 13. Meimi was improvising... So she used a cute Saint Tail doll holding the note to deliver it;
in episode 16, the note was on a giant screen outdoor;
in episode 32, the warning was on a banner;
in episode 34 she wrote it in the sky with fireworks;
in episode 43, it said that Saint Tail was going to steal Asuka jr. himself.
Asuka jr. protecting Saint Tail from Rina's tear gas attack in episode 7.
Asuka jr. tutoring Meimi in math. Sure, he had to be ordered to by the teacher, and he blackmailed her into promising she'd treat him to a baseball game before doing it, but she liked it. Plus, he did it even before she delivered.
Later, Rina (who found Meimi's ticket when she lost them during a caper as Saint Tail), offered to treat Asuka jr. at that same game. He refused, even when she offered to share the knowledge of Saint Tail's identity.
At the end of the anime version, at the baseball game:
Asuka jr. *knowing that Saint Tail made the game possible: "I guess we have to thank Saint Tail."
*Meimi blushes, and Asuka notices*
Asuka jr.: "Why are you blushing? Weirdo."
Meimi *embarrassed*: "You wouldn't understand! It's very hot!"
Meimi *thinking*:"I love you!"
If Genichiro and Eimi Haneoka are in the same room, chance is that one of these is happening.
Asuka jr. being completely fascinated by Meimi in a wedding dress in chapter 9 of the manga, and then trying desperately to change topic.
Asuka jr. standing out for Meimi and then being embarrassed by it when he explains to Saint Tail.
What, in Rina's attempt at catching Saint Tail, got our thief angry? In her own words to Asuka jr.:
Saint Tail: "If I'm going to be caught, I want to be caught by you!"
Saint Paulia Middle School has a tradition for their festival: girls get the lock of the locker of their beloved and hang it from the eastern fence of the school's roof in the hope he'll ask them to dance. And, in the middle of a caper taking place at school during the festival:
Saint Tail: "Would you mind... if I took this lock?"
And, incredibly, Asuka jr. asks Meimi to dance with him. By accident, sure... But then blushes when he realizes what he has done, and that she accepted.
Seira's declaration that if Saint Tail is arrested, she'll follow her.
The reason why an old woman wished to eat some particular rice gruel before dying: it was a dish made by her true love that she had been forced to leave due an Arranged Marriage.
And at the end of the episode, the reunion of the two lovers, after Saint Tail stole (her words, not mine) the boyfriend (now a famous cook) from the owner of the restaurant.
Saint Tail using a misunderstanding to help a girl in finding love.
At the start of episode 19, Asuka jr. was asked what he'd take with him to run away in case a comet was about to hit Earth. Later, as part of her plan to 'steal' a comet in episode 19 (actually kicking out the astronomers from the local observatory so the local kids would be able to see the comet as the previous director had promised them before being replaced), Saint Tail makes it appear that a piece of said comet has broken off and is directed against the observatory, causing the scientists to run away... And Asuka jr. to still try and catch Saint Tail, because he literally can't think of anything more important.
The bond between Meimi and Seira is apparently so deep that they can do the pre-caper heist at the same time from distance and without previously agreeing on a set time.
Meimi's worry for Asuka possibly getting off case in episode 30.
The story of Hiromi and his friend Mana the Pearl Dolphin.
Meimi and Asuka jr. alone together.
This episode also marks the start of Asuka jr.'s Love Epiphany: he first notices that Meimi and Saint Tail are practically identical in both looks and even aura, then after being asked why he chases Saint Tail, he tells Meimi that Saint Tail is his dream girl, and at the end, when asked by Saint Tail why he's chasing her, he tells her "You resemble the girl I can't stop thinking about!".
With this episode the second ending Upside Down is replaced by Yumemiru Melody, and its video, briefly resuming the whole story, fits in this category.
We're shown the first encounter between Eimi and Genichiro. Eimi, as a thief, was trying to escape the police, and Genichiro spontaneously decided to hide her in his apartment. But she was wounded and he had nothing to treat her, and she was threatening to make him pay if she got caught... Then Genichiro hid her under a mountain of roses conjured specifically for the occasion, and her heart melt.
Asuka jr. helping Meimi with her homework without being asked. He himself didn't know why he did that.
The end of Asuka jr.'s Love Epiphany. For two days he's been thinking about Meimi and what he told to Saint Tail, and, after Sawatari mentioned the legend of the treasure at the end of the rainbow, that's where he finds Meimi... And finally realizes he's in love with her. And, being Hot-Blooded and in spite of having a fever, has only one thing to say:
Asuka jr.: "I love you. I love you, Haneoka. It's the truth. I'm really happy that you're here with me, that my hand can reach you..."
Asuka jr. apologizing for his unwillingness to not engage into Sickeningly Sweethearts business, and Meimi saying she doesn't mind.
What does Rina have to say about the new situation?
In a twisted way, Rosemary's willingness to renounce her revenge against Saint Tail if she'll join her and Maju into stealing their way to prosperity. That, and the reveal that she adopted Maju: given she was already a talented enough thief to catch Rosemary's eye at her young age, she probably didn't have a good life beforehand.
Also, Saint Tail's reply: Asuka jr. is her jewel, and Rosemary must give him back.
Asuka jr.'s reaction to Maju pointing out that Saint Tail's warning notes are actually love letters.