Although they are longtime rivals, Shônen Sunday and Shônen Magazine just went through a huge collaboration project which lasted around one year (I think for the Americans here, this is roughly equivalent to when Marvel did crossovers with DC). Among other things, this led to a few games being produced, such as a fighting game on PSP and a role-playing game on Nintendo DS.
But the most exciting collaboration was this title. It is a baseball game which gathers casts from the numerous baseball series featured in the two magazines. So that means you get Major, Kyôjin no Hoshi, Ore wa Captain and all Adachi baseball manga series since Touch gathered in one cartridge. In order to appeal to a slightly broader audience, they also included a few other shônen heroes from their respective magazines as "special guests". Examples include Ippo, Ranma, Conan and the Negima cast.
Not only that, but since the crossover games were licensed to Konami, the game was developed by Pawapuro productions (the best baseball game studio in Japan).
The result is a great title which allows going through story modes for each series and creating your "dream nine" with your favorite characters from each manga. Want Aoba as your pitcher while Tacchan (Touch), Hideo (H2) and Akaishi (Cross Game) begin your batting order? You can! Unfortunately, each series is only represented by the main protagonist's team + a few popular characters such as love interests and rivals. You can unlock Momiji as a manager, in case you ever wanted to see that.
[edit] Also, one slightly disappointing detail for fans of this topic is that the Cross Game team is only "1st year" Seishû. Therefore, they are not as strong as the other Adachi teams, which is a shame considering that