I've Been Killing Slimes for 300 Years and Maxed Out My Level is an exemplar of the "slow life" isekai subgenre, where the point is that nothing much happens because the protagonist wants to spend their new life chilling out. In I've Been Killing Slimes, Azusa's motivation is explicitly tied to her death by overwork, so it generally feels as if there's a beating heart beneath all the hijinks. The emphasis is definitely more on comedy than on atmosphere, but overall this is a pleasant show in a way that can sometimes feel cathartic.

I do want to emphasize that the setting is absolutely flimsy and only works if you're willing to gloss over the artifice of its game-like logic. As the title succinctly explains, Azusa killed slimes for 300 years, which maxed out her level at an arbitrary point. The 300 years of time carry no weight whatsoever; Azusa reaches her peak within minutes of the anime's opening, which gives the impression that it all happened overnight. The anime gives very little indication that her experiences in those years impacted her outlook, given that the bulk of her recollections are of her previous life in Japan. Her unwitting path to super strength serves as both a punchline and a "slow and steady wins the race" message, but her believability as a character is sacrificed along the way.

The positive messaging about how patience wins the day is also undermined by narrative convenience. Not only does Azusa have the benefit of 300 years and immortality, she also has a skill that doubles her experience points. And for whatever reason, she's simply stronger than characters like Beelzebub who have not only lived an order of magnitude longer than her, but spent that time training diligently. Given how arbitrary the power progression is, Azusa might as well have gone into cryogenic sleep and had strength-enhancing drugs injected into her.

It's for the best that fighting is entirely besides the point in this anime. Any battles that do occur are brief and comedic in nature, existing more to establish character than anything else. The real point to the story is that there's more to life than work and linear achievements. Even within the game-like trappings, the friendship and found family themes come across loud and clear. When Azusa berates her newfound friend Laika for overworking herself, insisting that "working hard" shouldn't be talked about as a virtue, her words still manage to ring true in spite of everything.

I've Been Killing Slimes's modest storytelling ambitions are matched with modest visuals. The anime has bright and appealing colors, but otherwise does little to stand out in its direction or animation. One can't help but notice that despite wearing a distinctively oversized hat and cloak in the promotional materials, Azusa is rarely shown with them in the series proper. This was obviously to reduce the strain of animating her, which I can't blame anyone for; it would be cruelly ironic if this anime that decries overwork was created by overworked animators. I've Been Killing Slimes does what it needs to do to look pleasant on the eyes, and it doesn't extend itself more than necessary.

Overall, I've Been Killing Slimes is the definition of "harmless entertainment," the perfect thing to unwind to after a hard day at work. It may not be a standout in its genre, but it's a breezy watch that doesn't overstay its welcome. By introducing new characters almost every episode, the anime manages to keep its simple themes engaging for the entire duration. Just be warned that although the series has an all-female cast, the "yuri" angle is portrayed as comedic fodder rather than as romantic subtext. It's best to keep your expectations modest with this title.