I didn't really differentiate between Japanese and Western animation when I was a kid. I've watched Cardcaptor Sakura, Heidi and Pokémon that way. Heidi was the first, and that would be like when I was what, 7?
Over in 2006, I found myself languidly flipping TV channels and came across Animax and there was this commercial for Hell Girl, and I thought it was pretty damn spooky, sitting in the dark there. I caught an episode the next day (which just happened to be the first), and was impressed by the mature level, and also because the first episode was spooky (which weared off in subsequent episodes, except the goddamned Episode 13).
I also followed Trinity Blood then, and when I began to miss the episodes, I found them on the Internets and eventually migrated to Internat viewing.