Tomoe Tatsumi is a naive freshman who has just arrived in Tokyo. He gets lost looking for his hotel and runs into an older gentleman called Mitsugi Kurokawa and his friend Isogai who have just been out for a drink. Isogai -of course - throws up all over the poor boy and Kurokawa gets Tomoe's jacket dry-cleaned as an apology. He lets him stay the night at his apartment (since the directions were in the pocket of Tomoe's jacket) and escorts him to the university the next day. Kurokawa finds himself attracted to Tomoe's naive, scatter-brained charm and ends up kissing him goodbye one day. Tomoe seems to think it was some sort of foreign greeting and ends up moving in with Kurokawa as a tenant.
Kurokawa can't act on his newfound attraction though due to Tomoe's complete obliviousness and his insanely over-protective and homophobic older brother Souchi who doesn't want his brother in Tokyo at all. Things get much worse when Souichi discovers Kurokawa's true intentions.
- Art Evolution: Most noticeable - almost an Art Shift - between the first and second volumes, where the mangaka's style changes quite significantly and most of the characters start looking less Eighties (Tomoe's hair, for example, starts looking less like a mullet and more like just normal longish hair). If you count The Tyrant Falls in Love as an extension of Challengers, the change is even more pronounced - some fifteen years have passed between the two.
- Attempted Rape: Revealed as the reason Souichi is so homophobic - a professor at the university assaulted him, but Morinaga saved him just in time because they'd arranged to watch a movie together and he got worried when Souichi didn't show up. The guy was kicked out of the university, but no-one ever went to the police.
- Berserk Button: Just try mentioning "homos" to Souichi and see what happens. Partly justified, as his backstory includes a sexual assault by a senior professor that lead him to fear and hate gays. He's also a very overprotective brother, and blames Kurokawa for leading Tomoe astray.
- Blind Date: Isogai ropes Kurokawa into taking part in a group date with work to make up the numbers, but things don't go exactly to plan. The girl ends up being really into him, while Kurokawa still has eyes only for Tomoe but doesn't want to come out at work. Awkwardness ensues.
- Breakout Character: Souichi's popularity with fans ended up eclipsing both Tomoe and Kurokawa, leading to his own series The Tyrant Falls in Love.
- Camp Gay: Rick, to some degree.
- Cloud Cuckoo Lander: Tomoe is a complete and total one - he may be a roboticist, but that doesn't mean he has an ounce of common sense.
- Cloudcuckoolander's Minder: Tomoe and Kurokawa's relationship first kicked off when Kurokawa helped give Tomoe directions to the university and began wondering how a guy that naive could ever survive in the real world. Since then he's been pretty much looking out for him.
- Depraved Homosexual: All gays are like this in Souichi's eyes, espcially ones that dare to lay a hand on his beloved little brother.
- Dogged Nice Guy: Kurokawa is unusual for a Seme in that he is a genuinely nice guy and wants a relationship with Tomoe. This doesn't stop Souichi thinking that he's a disgusting homo beast who tricked his brother into staying with him.
- Drowning My Sorrows: Morinaga often goes to a gay bar to do this when Souichi's homophobia and mistreatment get too much.
- Foreign Farewell: Kurokawa kisses Tomoe as he's leaving on the train. When they meet again, Tomoe asks him if it was because he had an American step-father at one point. Kurokawa grudgingly says yes, the kiss was just an American goodbye, as he doesn't want Tomoe to realise his feelings towards him and be freaked out.
- Genius Ditz: Tomoe is studying Robotics but can't find his way to a hotel?
- Hair-Trigger Temper: Souichi gets violent whenever his brother tries to have independence or homosexuality is mentioned.
- Horrible Judge of Character: Tomoe is completely unaware of Rick's intentions.
- Hot Scientist: Souichi and his assistant Morinaga. Tomoe is something of a Cute Roboticist.
- Knight Templar Big Brother: Souichi. To the max.
- Mistaken for Gay: Happens to Isogai frequently, and he does in fact seem like one of the more flamboyant members of the cast. Ironic, considering he's pretty much the only reccuring cast member that isn't gay.
- One-Word Title
- Single-Target Sexuality: Tomoe and Kurokawa. Tomoe overlaps with If It's You, It's Okay.
- Straight Gay: Pretty much every character except Rick, who's a little more flaming, Isogai, who's Mistaken for Gay, and perhaps Souichi who is a Straight Gay but is very deep in the closet.
- Stalker with a Crush: Phil - he's followed Rick to hotels where Rick has then slept with other men before and still not given up on him. Overlaps a little with Dogged Nice Guy, as Phil had genuinely believed that they had a serious relationship when he flew out to Japan to meet him, wheras Rick saw it as "just sex" and a nuisance.
- Seme and Uke: Kurokawa and Tomoe respectively - mostly in appearance, the sex isn't explicit but it's implied that Kurokawa was on top.
- That Didn't Happen: Tomoe's homophobic brother Souichi after his kouhai confesses his love for him.
- Third Wheel: Rick is a Type A, once he starts following Tomoe and Kurokawa around in the hope of getting a chance to sleep with Tomoe.