Musou games are my guiltiest of all pleasures, right behind Justin Timberlake's music and having a certain affinity for the Daredevil movie.
I know. I KNOW. I'm a terrible person for at least two of those three. Nonetheless, there's just something about the systems in the Musou games - upgrading weapons and leveling up. I think it really clicked with me when I got Wei Yun to max level and started doing Chaos runs by SHOOTING A FUCKING FIREBALL FROM MY HEAD! It was just too much fun to be so goddamn powerful when I knew I could get killed so quickly.
With that said, I know jack nor shit about Fist of the North Star. Therefore, I may have to watch some of the anime and manga first before I jump into the game, just so I know what the fuck is going on.
Read at least half of the manga. It's fucking awesome, and the characters are interesting as fuck. Specially Raoh. He's awesome.
Yeah, either read or watch half the series. It's much better than it has any reason being and definitely worth the time.
For something that has such a simplistic and "ultra-macho" storyline, it's really, really great.
EDIT: Also, the boxer from the second half is really cool. Nothing compared to anyone from the first half, but hey...