I saw it probably about 8 years ago, if not more, but it wasn't super old at the time, I'd say it's from the year 2000 or so at the earliest. It's about a guy (teenager, I think) who ends up in a fantasy world (no idea how) that is threatened to be destroyed by something. I think the way it could be saved was by collecting some gems or pearls or something that give their owner great power.
When he arrives there, he has to choose sort of a "class", if I remember correctly (I think it was sorcerer, or magician of whatever). There's a couple of scenes I remember quite distinctively. The first was pretty early on, when they were on the outside somewhere (in a snowstorm, maybe) and get attacked and one of his allies at that point dies. The second is in some kind of ruins or temple and involves huge vines with thorns and stuff.
I'm also pretty sure that, at some point, the protagonist betrays his allies to get more powerful himself, which is pretty much the point I'm most certain to remember correctly to some degree. Lastly, I believe the protagonist had blond hair, but that's half guessing.
Oh, also, since I am from Austria and saw it as a kid, I can 100% say it's got to have a German translation, so it' most likely not a very niche or unknown one.
EDIT: As the comment suggested, I thought of some more details that might be helpful.
- I don't think it belonged to any anime series, but I'm not sure about it as I wasn't much into anime back then yet.
- It had a Japanese animation style.
- I saw it on TV.
- I think it was rather brutal at times (blood etc.), so it was likely aimed at at least teenagers, not little kids like I was.