Yes, there is. As Sage Rat mentions, there are two separate titles (interesting, thought this was a ploy they thought up for the U.S. release), though having read neither, I can’t say which one is “better.”
In the US, it’s Trigun vol. 1 & 2 (was 3 volumes in Japanese) and then it segues into Trigun Maximum. The reason for the name change (which occurred in the Japanese as well) is that the author changed publishers after volume three of Trigun and so the series title was slightly altered.
There are a couple of other things I dont quite understand. spoilers for whole series:
-What is the purpose of attaching Vash’s arm to Legato? Is that where Legato got his powers?
-Why are the Gung-Ho guns referred to as deamons? Are they something special? Only Legato seems to have any real superhuman powers.
-How does Knives kill Wolfwood’s mentor? He displays some sort of black hole power… that is never used again. What?
Are the spoiler tags really necessary for a topic saying ‘explain this series to me’? Oh well.
In the manga, he had powers before he met Knives (this is explained somewhere around Trigun Maximum 13; so far 8 is the latest translated volume. I’ve been keeping myself in the dark about the manga, since I knew all the anime spoilers beforehand). In the anime, it’s also likely that this is the case. Knives would have no reason to spare him oterwise. Attaching Vash’s arm to Legato was possibly a way of boosting Legato’s powers… and if Knives couldn’t have Vash at his side, then his arm would just have to do.
Hard to tell, at least in the anime. Zazie certainly has something odd going on with his purple lizard eyes, and Dominique’s eye might be something supernatural or simply an odd bit of lost technology.
Your guess is as good as mine. Maybe it was the action of one of the Plant bulbs that were in the area. It’s shown that he can control them.
I’d recommend checking out the manga, even though it’s extremely confusing to read and the timeline is slightly different at the best of times. Think of the anime and the manga as different stories with the same characters-- they’re both equally canonical, even if they don’t gel very well.
[spoiler] However they all seems to have special fighting skills or gear or particular traits that make them exceptional or abnormal. Apparently Knives sought out as minions people who were also “different”, and got to do some alterations on them.
A lot of “left unexplained” bits in the animé seem to be glosses (due to time constraint) of things covered in the manga, but I can’t tell to what extent as I have not read anything but fragments thereof. [/spoiler]