Challengers by Hinako Takanaga has to be one of my favourite mangas ever. Along with Black Butler and Loveless of course. :)
Some people complain that the artwork isn't as good as the author's latest works, but I would kill to be able to draw like the art-style of Challengers! It looks kind of retro in a sense, but goes through a bit of a revolution of art style... In short I love it.
The story follows a Freshman student called Tomoe Tatsumi, who studies robotics in a really good universtity. Despite being really intelligent in his studies, he seems a little bit half-witted at times (but cute as holy hell). As Isogai put it to Kurokawa-san, he's a 'laim-brained sweetheart' XD
Tomoe meets Mitsugu Kurokawa, a salary-man living in Tokyo, when Kurokawa's friend, Isogai, throws up on Tomoe (they're drunk by the way XD).
The freshman doesn't have a place to stay, so Kurokawa offers him a rent of his apartment, much to Tomoe-kun's brother's displeasure. Who, by the way, becomes quite an important character later on in a sequel called Koisuru Boukun. Kurokawa-san act's as Tomoe's Landlord despite having romantic feelings for the boy.
He tries to make Tomoe understand those feelings by kissing him goodbye, but due to Tomoe's umm 'laim-brainedness', he misunderstands the kiss as an American custom, and so, Kurokawa has to jump through even more hoops to get through to him!
I can honestly say that I loved all the characters, except for maybe the lady at Kurokawa's work, who found out he was homosexual and took it upon herself to try and 'rehabilitate' him. Creepy!
Challengers is cute, funny at times and lighthearted. I would defiantly recommend this manga to any lover of shounen-ai!