There isn’t really any reason that a Christian couldn’t watch anime, unless the particular anime a Christian is deciding on happens to heavily feature or promote actions/things/etc condemned in the Bible. In that case it would still be the Christian’s choice but it would make logical sense for them to choose not to watch that particular one. But there isn’t anything condemning animated entertainment as a whole.
Because Nintendo is a vexatious litigant that weaponizes the legal system in an attempt to bankrupt their opponents.