Pokémon is one of the most popular and well-known media franchises ever, with the Pokémon anime being many American kids' first exposure to the medium. Over time Pokémon has worked hard to appeal to both new young fans and its older, long-term fanbase. But it still has a reputation as a children's franchise. However, Pokémon has shown several times that it can talk about serious topics in a nuanced, understandable, and emotional way. And The Birth of Mewtwo is the perfect example of this.
Source：https://www.cbr.com/pokemon-mewtwo-full-origin-story-uncut/
