When half-naked shrine maiden Nonoa suddenly disappears, her childhood friend Yamato and an angel, Sera are thrown into a panic! Sera finds it strange that Filika, a devil, disappeared at exactly the same time.

Is Japanese animation better than American animation? Why?

The animation style is different, but I wouldn't compare the animation at all.
It's the storytelling. While both Western and Japanese animated movies (Pixar and Disney being the representative of the Western, and Studio Ghibli being the representative of the Japanese) tend to be family-themed, a lot of Studio Ghibli films has a much more matured take to it (Grave of the Fireflies, Princess Mononoke, The Tale of Princess Kaguya) compared to most of the American animation films (Up being the only one with a more matured take coming to my mind). But there's the TV too. See it this way.
American animation mostly focuses on these three aspects: Family animated movies (Disney, Pixar, etc.) Adult cartoons, or animated sitcoms (Simpsons, South Park, Family Guy, etc.) Children cartoons (SpongeBob, Tom & Jerry, Looney Tunes, etc.) While Japanese animation has a much broader general audience, being: Anything by Studio Ghibli for family viewing. Anime series that basically covers all genres for all age type. It's rare to find some sci-fi thriller in animation in the America, and it is unheard of for an animated film/series with a psychopathic megalomaniac that wants to rule the world and is actually the main character of the series, which makes you want to root for that basically evil guy, but these are just a few found in Japanese animation. To end this, American animation targets audience of families, adults/teen humour, or children. Japanese animations' targeted audience is not limited to a specific category, and they produce tons of new animations every year for the TV, therefore having a wide range of genres and targeted audience for each series, which allows more creativity to flow in the storyline, making some of the series having a potential to rival even the best Western live-action movies and TV series, but with animation, anything is possible, unlike live-action. And that is why I think, in some aspects, Japanese animation triumphs the Western animation.