Fans of anime will love That Time I Got Reincarnated as a Slime the Movie: Scarlet Bond, directed by Yasuhito Kikuchi. While those unfamiliar with the series may be left lost (with the large band of characters and the unexplained lore), the story central to the movie is new with characters that were created specifically for this installment.
The protagonist of the film is a survivor of the Ogre race named Hiiro who is saved from death by Queen Towa, monarch of a small gold-mining nation named Raja. But the Queen herself is sick as she spends each day removing cursed toxins from her nation's water source. This use of her power has left her weak and sick from the toxins. Hiiro feels indebted to her and vows to find the source of the curse as well as a cure to save her from death. He travels to a nation with its own unique history, called Tempest, to ask them for their help. There he finds the series protagonist, Rimuru, who comes to their aid so they can unearth the mystery of the poisoned town and save the life of the benevolent queen.
For those not initiated into the series before watching the film, the protagonist of the series is Rimuru Temptest, a corporate cog who died saving his friend and was reincarnated into a slime. Within the series, he continually levels up and becomes the leader of his own nation as well as becoming a demon lord. In addition to collecting new abilities and adventures, he also gains a loyal band of friends. His kindness, compassion, intelligence, and powerful magical abilities makes him someone to look up to but also someone who people come to in order to solve their problems-which is why Hiiro goes to him in the movie.
The movie is voiced by the same cast of actors who voice the series. In addition, are voice actors Jonah Scott (English Dub) and Yuma Uchida (Japanese cast) as Hiiro, Riko Fukumoto (Japanese cast) as Queen Towa, and Subaru Kimura (Japanese cast) as Lacua, a peddler who visits Raja. The story for the movie was written by Fuse which means that the film is canon to the series.
The themes of friendship, loyalty, and the different types of bonds which can be held between one another are clearly depicted on screen by the main characters. There are a couple plot holes within the movie, but nothing that takes away from the story until fans try to analyze the film after it ends. The action is intense and the physics "jiggly" enough to keep moviegoers immersed in what is going on.
While watching both seasons of the anime isn't necessary, That Time I Got Reincarnated as a Slime the Movie: Scarlet Bond is best watched by those who know the ins and outs of the lore. Though, even watching a couple summary videos on YouTube can help those who are not as familiar with the series, yet are interested in the film.