After having successful games with Marvel and SNK, Capcom then teamed up with Namco to create a new title. However, instead of being what everyone thought (a one on one fighter) Namco X Capcom was instead an RPG featuring many characters from both Capcom and Namco sides. It was released in 2005, exclusively for the Playstation 2.
The story is set in Japan in 20XX and revolves around 2 new characters, Arisu Reiji and Xiaomu, as they are sent in to investigate a "sleeping sickness", but as they start their investigation they soon find out that something much bigger is happening and characters from different time lines are suddenly appearing. Arisu and Xiaomu team up with various different characters to stop the rising threat. Which is just a big excuse to get a ton of Capcom and Namco characters together.
Final Fight wise, this game has both Guy and Haggar in it, both of them are playable characters. Guy can team up with Ginzu (the ninja from Captain Commando) and Haggar has his classic moves like his spinning clothesline. Namco X Capcom didn't sell very well and was only ever released in Japan. There has been a lot of speculation to why it wasn't released in American or Europe, such as Capcom and Namco arguing over profits, the fact that Namco's non-Tekken characters aren't well known overseas and Sony's refusal (at the time) to sell 2D games at full price for the PS2. No matter what the reason was, this game will remain a Japanese exclusive title.