Hikari knows what it feels to always be second to someone else. After all, she's still ranked second in the school, meaning she's still failed to beat Kei Takishima at something: something she's been trying to do since they were six years old. She even followed Kei to Hakusenkan just to beat him, which costs her family a lot of money. It's not that she's incompetent, however: Hikari is still incredibly strong, incredibly smart, and incredibly pretty. She's just thatoblivious to Kei's feelings for her.
Action Girl: Hikari is frequently shown training, and it shows — the only times she's collapsed involved injury/illness combined with a rather large amount of exertion (after competing in several matches). Moreover, the only time she's lost any of those are, of course, when up against Kei. Further, she's yet to lose any physical fights she's been in, though you'd think she was made of cracked glass the way Kei reacts to the prospect of her fighting.
Berserk Button: Anyone claiming that she's second-best. Kei intentionally invokes her ire most often by constantly calling her "Miss Second Place," but Yahiro isn't above teasing her with this. Taken Up to Eleven in the final competition between Kei and Hikari in the series - Kei has to find the real Hikari amongst a host of impostors, and Kei gets creeped out when they all respond appropriately to "Miss Second Place" in unison.
Can Not Spit It Out: Mere minutes after realizing that she's fallen for Kei, she hears someone say that "the first one to fall in love loses." As she continues her obsession with defeating Kei in something, she absolutely refuses to be the first to confess.
Chapter 53/54 in the manga, she does spit it out. MUCH EARLIER THAN THE ANIME.
Determinator/Plucky Girl: Hikari will not give up, no matter how many times she's been defeated, at beating Kei. She won't give up on anything else, either, though her intelligence and strength result in her not needing to continue for too long generally.
Oblivious to Love: Oh, so much. She's so focused on her and Kei's rivalry that she can't even take a hint.
Selective Obliviousness: Only towards her, though. She quickly perceives someone's attraction to someone else - more than one Face Palm ensues after people realize she sees everyone's romantic intentions except Kei's.
So you're the handsome elder son of the filthy rich CEO of the Takishima Corporation. You're ranked first in your school and have a natural talent for everything you do. You excel in every single subject, from athletics to mathematics. Everything just comes easy for you, doesn't it? Oh, wait. That's not you. That's Kei. And it's true: the only problem poor Kei has is that Hikari just doesn't get his feelings for her.
Can Not Spit It Out: You know, for being as smart as he is, you'd think Kei would have the brains to just explain how he feels if he was really interested in dating Hikari (particularly given how distressed he gets at times by her cluelessness).
The son of two famous musicians and Megumi's younger twin brother, Jun is ranked third in school. Because of his upbringing he loves music more than anything else: it's just that he has little to no talent for it. Jun, like Megumi, is fiercely protective of Ryuu because he's been kind to them since they were children and is always looking out for the two of them. Generally quiet and unassuming, whenever he's kissed by a girl, his Split Personality ("Dark Jun") comes out, giving him the ability to charm all women effortlessly. This was the result of a TV program he watched as a child. Jun is terrified of this because it caused the girl he was dating to dump him in disgust. And the reason he falls for Sakura is because she's willing to accept him despite this.
Jun's older twin sister, Megumi is ranked fourth in school. Like Jun, she values music more than anything else, and is a singer. She rarely speaks to preserve her voice (and her singing is ''quite'' powerful as a result. However, her voice is gorgeous when she sings in an open area.. Also like Jun, she's very protective of Ryuu for the same reasons her brother is (ie. during tests he's making sure they don't fall asleep, etc.) Later in the anime she develops a crush on Yahiro. In the manga, this is after pretending to like him to make sure he doesn't mess up Akira and Tadashi's relationship.
Ditzy Genius/Brilliant but Lazy: On the other hand, he's apparently rather competent: he's ranked fifth in school and it's hinted he could be higher, he's quite athletic, and knows his way out of awkward situations. On the flipside, he has little to no tact, common sense, or wit. Most of the time.
Akira is ranked sixth in school and is the daughter of the owner of a famous airline company. She has a talent for cooking and is the one who whips up the group's afternoon snacks. She is very fond of Hikari and usually won't do anything unless Hikari agrees to it. She was good friends with Kei and Yahiro as a child, except that after Yahiro drove her only friend Sayo away she began hating him for it. She enjoys beating Tadashi up and they end up as the series' first Official Couple.
Adaptation Dye-Job: Her hair was quite black in the manga, but is changed to purple in the anime.
Seventh in their grade, Ryuu is the son of a sports car company's CEO. He is very good at handling children, animals, and plants. The twins adore him, primarily because the three of them have been together since childhood and since meeting them he's always been looking out for them.
An old friend of Akira and Kei's, they haven't seen much of him after a mutual falling out that no one likes to talk about. A seemingly affable young man with a sinister streak and a love of screwing with people's heads, Yahiro serves as the main antagonist for the first part of the series. A master manipulator, Yahiro does his utmost to conceal his real agenda from everyone, all while doing his best to look like an unsympathetic jackass.
Badass: He actually scares Kei. That's gotta count for something.
The Beard: In one arc in the manga, Megumi has told her mother that she will bring her boyfriend to a concert that the family will be attending. Only thing is, she doesn't have a boyfriend. Guess who gets roped into filling this role?
Broken Ace: He's a toned down Kei with a side of self-loathing.
Defeating the Undefeatable: He actually managed to beat Kei in a game of tag when they were younger by locking the door while Kei was counting. Slippery.
Easily Forgiven: Averted for some time, to the point where when Jun and Ryu catch him with Megumi violence nearly ensues. Also completely averted with Akira, as it's hinted that she's refused to speak with him for seven or eight years due to her anger.
Evil Genius: He's at least as smart as the members of the Special A.
For the Evulz: Acts like this is his motivation for screwing with Akira and Kei.
Heel-Face Turn: After Akira gets together with Tadashi and Megumi takes an interest in him.
Hidden Depths: He really does value both Kei and Akira and is willing to appear the villain to both of them to keep them from getting hurt.
I Want My Beloved to Be Happy: His entire motivation. He drives off anyone who poses a threat to Akira while taking the blame so she'll never know she was betrayed. After she gets together with Tadashi he promptly drops out of the picture.
If You Ever Do Anything to Hurt Her...: He mentally remembers doing it to multiple people in regards to Akira in the past, and he does it in-series to Tadashi, who isn't threatened at all by it (Yahiro assumes, initially, that it's because Tadashi is an idiot).
It Amused Me: In the manga, he claims this is why he hangs out with Megumi and helps her with her singing. Right...
Zero Approval Gambit: He'd rather have Akira focus her hatred on him, completely destroying their friendship, than admit he was trying to protect her from a Gold Digger friend. He later pulls a similar routine on Kei.
Older Than They Look: He looks like an extra-tall version of Sui, although he's in his late thirties.
Wrestler in All of Us: He's a huge fan of pro wrestling, and attempts to wrestle with Hikari whenever they meet as a greeting. Stretching back, the entire plot is set in motion because of his wrestling fandom. He's a part of the same wrestling fan club as Hikari's father, who invited Satoru and Kei over to visit... which resulted in Hikari challenging Kei, losing to him for the first time, and starting her obsession.
Tsundere: Unusually, as a reaction, not as a default. She's more tsuntsun towards people who act stoic towards her (like Kei), but she has no problems opening up if people are acting warm towards her (she positively adores Hikari).