The permissibility of watching anime depends on its content. If the anime promotes unlawful content in Islam, such as witchcraft, disbelief, or foul language, it is impermissible to watch. Watching anime that gives haram thoughts is also considered haram. However, viewing cartoon images of the opposite sex without desire is permissible. It is important to avoid anything that may cause harm or promote un-Islamic values.

And Allah knows best.

Sources:

• Ask Imam – Are watching cartoons and animated movies permissible?
• SeekersGuidance – Is it permissible for me to watch anime?
• IslamQA – Watching animated movies and shows that contain matters contrary to Islamic belief