Tenshimitsu : And... I hate the overall gaming tendency to "darken" the character... it's always the case with many heroes. Like e.g. Prince of Persia. A nice, bright hero turning to be some kind of demon. I don't like it at all.I see a strange continuum going on between Tekken and Soul Calibur Yoshimitsus. To a certain extent, both stories have a lot in common, ie. destruction of the clan, and somehow all this comes down to the same thing: the Sword.
I don't mind the dark theme they've got Yoshi into, I had hard time taking him seriously when all he seemed to do was fool around. What I don't want him to lose is his unique sense of humor and that childish smart-@$$ attitude.
Tenshi, the Sword Yoshimitsu carries is evil, despite all, right? And to keep the Sword "under control" it needs to be calmed with blood of namely Yoshimitsu's enemies, unless I'm very greatly mistaken. What I don't think is that Yoshimitsu would go around killing people to keep the Sword under control, which of course results in the Sword gradually robbing him of his sanity.
Theory: this is the reason of his gradual change to dark theme, but there is still enough left of his sanity/humanity/you-name-it for him to realize what's going on and do something about it. Now, I don't know the story of Soul Calibur IV, but I'd be surprised if it had nothing in common with the Tekken story of Yoshimitsu's.
In a nutshell, I think that Tekken and Soul Calibur are somehow presenting Yoshimitsu's life cycle in Dark Ages and in modern day; hundreds of years have passed and he's still struggling with the same issues.
*heaves* I think that was about everything. Second theory is that Namco considers dark-themed characters more media-sexy than cheery ones.