The main protagonist and a second-year member of the track-and-field team, just so he can find a convenient excuse to peek at girls in swimsuits at the school pool, which is nearby the track oval. Wishing to get rid of his "PR fašade", one night he makes an offering to the "Stony Cat" together with another wisher, Tsukiko Tsutsukakushi... and now he cannot help but air what's on his mind, no matter how perverse.
Accidental Hero: Some of his gripes about his PR fašade is that he tends to do awesome things without even intending to.
First Kiss: With Azusa. Tsukiko is not amused that the former has already beaten her to it.
Forgotten First Meeting: Doesn't remember that he already met Tsukiko a year prior to the start of the series, as she was wearing a mask then. Turns out this is a consequence of his wish to the Stony Cat when he was young, as he also doesn't remember Tsukushi and Emi despite meeting them before the story.
Gag Penis: The euphemism compares it to an elephant trunk.
Laser-Guided Amnesia: Made a wish to give Tsukushi his memories of her mother ten years prior to the story. It causes him to lose memories of any girls he meets that are separated from him long enough. This causes lots of problems throughout the series for several girls.
Loose Lips: He just can't keep his big mouth shut, leading to unnecessary trouble.
Lovable Sex Maniac: Post-wish. Also deconstructed, as he finds his world being turned upside-down by his complete inability to sugarcoat his perverted thoughts.
Nice Guy: Perverse streak aside, Youto is actually a pretty affable, good-natured boy who's more than willing to put his dignity (as well as his own memories) on the line if it will ultimately help the people he genuinely cares for, such as Tsukiko and Azusa.
Oblivious to Love: Has no clue about Azusa's affections for him. However, after stealing her first kiss, her affections become so overt that it's impossible for him not to notice.
A first-year girl with a shy, fragile disposition, she wished to become more mature to the "Stony Cat" together with Youto... only to discover that she has become completely unable to make facial expressions.
Silently scratches Youto's DVD collection featuring busty women with a pair of scissors. And then perks up the moment Youto mentions his tastes have "changed", going as far as to inquire how they have changed. Just for reference, of course.
When cleaning up his room, she throws out all his "material" featuring busty women, yet keeps those with petite girls.
In episode 11, while trying out a bra, Youto accidentally walks in on her. After she uses it to cover his eyes, he says that they're too big for her, followed shortly by her knocking him unconscious for bringing that up.
Beware the Quiet Ones: Despite being unable to express herself, Tsukiko is surprisingly aggressive in her interest in Youto, and accepting towards his... tendencies. And in Episode 6, after watching Azusa and Tsukushi do a Lover Tug of War on Youto, she mentions how she hates people who waste food. All three of them immediately stop, and begin eating and mentioning how awesome the food is.
Big Eater: Frequently seen with various kinds of snacks in hand, and seems to prefer her food super-sized.
Broken Bird: Shows some issues with her relationship with her sister Tsukushi.
Clingy Jealous Girl: Although more subtly than Azusa, she also doesn't like it when Youto is spending time with other girls, especially when she's around. And in episode 12, she's not happy to hear that Azusa beat her to the punch with Youto's First Kiss.
Not so Above It All: In episode 6, Youto catches her singing a tune he mentions he was singing earlier when he walks into the kitchen and sees her making food. He then sees her wearing his shirt, and she mentions that she was merely using it as an apron because she couldn't find hers. Youto then mentions that in an earlier Dating Sim game he played, one of the girls wore the shirt of their love interest so that they could smell them and feel closer, which causes her to blush and try to change the subject.
Broken Bird: Was the victim of bullying in her previous school (or rather, gravely misunderstood her schoolmates' pranks which were meant as friendly overtures) and has since put up a Rich Bitch fašade.
Clingy Jealous Girl: She doesn't like Youto paying attention to other girls, such as when Tsukushi attempts to flirt and seduce him openly in front of her in episode 6.
Covert Pervert: Secretly wants Youto to see her in a bikini, and do various "stuff" to her.
Cry Cute: The end of the first half of Episode 3, after Youto apologizes to her for lying to her into facing her past.
Dude, Where's My Respect?: While it's technically the cat god statue saying this to Youto, she laments about how she puts up with and does all of these favors for him, only not to get anything meaningful in return. Youto then "pays" her back with a kiss.
Expy: Being a petite blonde that puts up an "ojou-sama" facade/lifestyle to hide her lower class status makes her quite similar to Mio Aoyama from The World God Only Knows.
Flowery Insults: Tends to break into bursts of continuous, creative insults based on animals (e.g. calling him a "stupid spotted hippopotamus" or a "big bald bear who betrays all the bunnies you bluff") whenever she feels displeased at Youto.
Tsundere: Type A post-wish. Also deconstructed, as it turns out not only did she inherit Youto's "PR fašade", but also as a coping mechanism for being bullied back in her previous school (or so she thought). After she and Youto revert their wishes, she becomes Type B for the guy. After getting her first kiss stolen by him, she becomes dere-side-up.
Covert Pervert: In episode 8, when Tsukushi visits Youto's house, she looks at one of his picture albums. At one point Youto asks her why she keeps taking pictures of him out of the album. She casually dismisses it, saying it must be her hand acting on its own. If you pay attention to her hand, she's actually stealing them and putting it inside her shirt. She later casually mentions that rubbing her face with said pictures in episode 10 while discussing a possible Forgotten First Meeting with him.
Gag Boobs: They are prone to Gainaxing, and are subjects of various jokes throughout the series.
Youto: "Hey President, since which grade did your breasts start to grow?" (Cue smackdown)
Hair-Trigger Temper: As Youto finds out, talking to her is like treading on a minefield, especially when Tsukiko is concerned.
Innocently Insensitive: They just wanted to make friends with Azusa. Unfortunately, their methods backfired horribly, and they never knew of its consequences until Youto told them right in their faces.
Clingy Jealous Girl/Green-Eyed Monster: She acts hostile towards Youto largely because she hates how close Tsukushi is to him and even prefers him to succeed her post (it also doesn't help that she is hinted to have a crush on her). Later novels reveal that she also resents the ease with which Youto makes friends, in contrast to how her cold personality puts others off.
Genre Savvy: Of her teammates, she is the first to notice Tsukiko, Azusa and Tsukushi falling in love with Youto.
Hypocritical Humor: Loves to snark at Youto's perversion but does it using incredibly explicit vocabulary that manages to creep every team member out (especially Youto), and has an underwear fetish.
Jerk with a Heart of Gold: Very much unnecessarily rude and hostile, which contributes to her solitary reputation. Nonetheless, Tsukushi is the only person she shows due respect, and is willing to do anything to make her happy, even if it means swallowing her ego and going on a proxy date with Youto, whose kindness ultimately reaches her, making him Mai's first true friend.
Schoolgirl Lesbians: Strongly implied in the last episode when she goes to the amusement park with Tsukushi and the other main characters, along with her holding a body pillow with a picture of Tsukushi on it during episode 12's Eye Catch.
Parental Abandonment: 6-year old Tsukushi believes Tsukasa essentially did this, because she never once visited them in Italy. Turns out she was wrong, and Tsukasa couldn't go because she was too ill to travel, but tried to show her love for them by making clothes, which she used 6-year-old Youto to test on.
Tsundere: Type A towards young Youto. She kept telling him off, but enjoyed his company.
Jerkass Genie/Jerkass God: More interested in making wishes "come true" and expecting its "customers" to keep their own end of the bargain than considering any grave consequences its methods can bring.