“Sanda” unfolds in a dystopian future where Japan’s government has resorted to extreme measures to counter the declining birth rate. The story follows Kazushige Sanda, a 14-year-old with the supernatural ability to transform into his legendary ancestor, Santa Claus. After braving the cold to help a child on a snowy Christmas, he requires only to don something red to activate his powers. When he hesitates, his classmate, Shiori Fuyumura, desperate to summon Santa, stabs him, ensuring his shirt turns red with blood. The narrative only becomes more bizarre from there.

Based on a manga by Paru Itagaki, known for “Beastars,” “Sanda” is animated by Science SARU, the studio behind “Dandadan.” It’s available for streaming on Prime Video globally, with the series finale set for December 18. If “Sanda” maintains its momentum, it could become a beloved unconventional holiday classic.

In Itagaki’s rendition, Santa Claus is portrayed as a superhero, a muscular old man immune to fire from frequent chimney descents. Other traditional elements of Santa are reimagined creatively: his ability to know if someone is naughty or nice translates to a built-in lie detector, causing objects to fall when lies are told, and sleigh-blades emerge from his feet. Additionally, Santa possesses a remarkable healing factor, surviving even headshots.

As if being a middle schooler and Santa simultaneously wasn’t challenging enough, the world of “Sanda” complicates growing up even further. With so few children, society strives to keep them young for as long as possible. Kids are born into arranged marriages, and sexual education is barred at Daifuku Welfare Academy, which follows a “trauma-free curriculum.” Medical advancements have removed the necessity for sleep, and children are prohibited from sleeping to delay physical maturation. Fuyumura, defying this rule, experiences growth and navigates deeper questions about her identity and sexuality.

While Santa’s powers resemble Wolverine’s, the superhero whose Sanda’s circumstances most closely parallel is Shazam/Captain Marvel. Rather than saying magic words to transform into an adult hero, Sanda becomes Santa by wearing red and changes back to Sanda by eating “Bratty Bean” jelly beans. What makes this transformation extra complicated is that it’s not only physical but psychological. Santa must protect all children and can’t fall in love with them, while Santa’s adult mindset starts to override the still-young Sanda. It makes for a strange coming-of-age metaphor of the type which anime excels at; if you’re a fan of “FLCL,” “Sanda” delivers similar vibes in addressing the confusion of adolescence via action-packed insanity.

As if being simultaneously a middle schooler and Santa wasn’t hard enough on its own, the world of “Sanda” has made it extremely difficult for anyone to grow up. Because there are so few kids, society tries to keep them kids for as long as they can. Children are born into pre-arranged marriages and sexual education is verboten in Daifuku Welfare Academy’s “trauma-free curriculum.” Medical advances have eliminated the need for sleep and kids are banned from sleeping to slow down physical maturity. Fuyumura has broken this rule, experiencing growth spurts, and deals with broader questioning of her identity and sexuality.

The sheltered status of children goes so far in this future that it’s not a crime for kids to kill adults; young murderers take special classes in the school’s basement. Adults in this world are obsessed with their own appearance of youth through extreme plastic surgery. Headmaster Hofumi Oshibu (Toshihiko Seki) is 92 years old and goes to extreme lengths to seem younger, replacing almost all of his organs with cybernetics. Only the wrinkled skin on his hands indicates his true age.

As you would expect from the creator of “Beastars,” “Sanda” goes to some dark and uncomfortable places. It contains bloody violence and complicated sexual themes, so it might not fit into every viewer’s Christmas stocking. However, for anime fans seeking holiday viewing that challenges as well as entertains, it’s a streaming gift well worth unwrapping.