Critical reception
Digital Spy's Ali Griffiths described in his review of the series' premiere that the series makes up a group affectionately known as the "dark trio of shōnen" by anime fans along with Jujutsu Kaisen and Chainsaw Man (coincidentally, all animated by MAPPA) due to their similar tone and themes, especially compared with their peppier peers. Ali praised the show's character-building, action, animation, visuals, humor, and the handling of Gabimaru's versions of his story which tells about "how he's feeling and what he wishes he'd done differently". He felt that some fans might found that the opening episode of the series was a little slow, but stating that "the way it centers the backstory of its protagonist and immediately emphasises the relationship between Gabimaru and Sagiri is emblematic of the kind of character-first action show they're hoping it will be".
MrAJCosplay of Anime News Network reviewed the first three episodes of the series. While praising the anime for its colors, sound design and animation, he considered Sagiri's character as "strong" and endeared on how she can see right through Gabimaru's façade. He felt that "her decision regarding walking down the path of an executioner and characterization as a stickler for the rules wasn't the direction he expected the show to go". Her introduction in episodes two and three was considered to be a "little inconsistent", although he needs more time to root her. He also noting that Gabimaru was one of his favorite characters, while he found the character's backstory as "sweet" due to the subversion of his mentality.
Adi Tantimedh of Bleeding Cool in his review of the first two episodes gave them a 8/10, feeling that they had a "stylish opening chapter to a brutal, bloody journey of death and redemption as a ninja is forced to take a suicide mission to find the elixir of eternal life, melding the samurai saga with a supernatural thriller drawing from Japanese folklore". While Den of Geek's Daniel Kurland would rate the first episode of 4 out 5, writing "quite the bloody affair and is absolutely obsessed with death. That being said, this is far from a callous series. If anything Hell's Paradise doesn't criticize this brutal behavior, but rather emphasizes how there's a right and wrong way to slice off a head and bathe in blood".
