DO NOT READ IF YOU DON'T WANT SOME SPOILERS!!
Now I'm a fan of the Rorouni Kenshin Series and an anime otaku (fan) but when I first saw the Trust/Betryal OVA, I was blown away. The animation is superb and the storyline is much darker and less comical then Rorouni Kenshin. Not that I don't like funny but seeing Kenshin kill mercilessly is something else that should be seen to fully appreciate the series.
The first part (Trust) begins with a stunning crafted (and violent) scene where Shinta (Kenshin) sees his entire slaver "family" killed by bandits. His master-to-be, Hiko, saves him and changes his name to Kenshin.
We skip a couple years and see Kenshin in his late teens (17 or so) where he's an assassin who kills political members. But his assassin career doesn't last, during a mission, he recieves the first slash of his X scar. He meets Tomoe, the fiancee of the man who gave him the scar, soon after. As his comrades are killed in a raid, he and Tomoe escape to the mountains where they become lovers.
The ending is extremely sad where Kenshin, after learning that Tomoe was working to kill him, stumbles blindly through the snow to find her, still contemplating whether to kill her.
He gets the slash on his back we see later in the series turning that time and is almost beaten before he finally gets the sense to swing and kill him. But with the same blow, he kills Tomoe who was trying to protect Kenshin from his opponent's final strike. Just before she dies, she, having learned that Kenshin killed her fiancee, completes his X-shaped scar, before her body falls still.
Kenshin cremates Tomoe in a small house and walks away, his last defense against his killer instinct taken away by his own hands.
This is an overall triumph in Japanese animation. The violence, extreme and graphic at times, is not a reason to skip such a terrific anime. If you are a true Kenshin Fan, you need to see this.