Sanda

The story is set in a near-future Japan, facing an era of extremely low birth rates. Children are treated as national treasures and are cared for and protected by adults in boarding schools. Santa Claus, who gives children hope and dreams, is considered a dangerous person and is targeted for elimination.

On a snowy December 25th, middle school student Sanda Kazushige's life is threatened by his classmate Shiori Fuyumura. Having learned that Sanda is a descendant of Santa Claus, she is hoping that he will grant her a wish. "Santa, please find my friend." Fuyumura's wish is to find her missing best friend, Ichie Ono. To protect the children, Sanda decides to become Santa Claus and fight against adults!

(Source: Official YouTube, translated)

AniMojo is the best site to watch Sanda online and download Sanda for free. You can also find Science SARU anime on AniMojo website with English Sub/Dub.