It's honestly impressive that Akitsu Maru is as popular as she is, given that her in-game art is pretty amateurish.
So far her design is flawless when consider what KC aims for, She stands out both physically and in voice, she is easy to draw as well, proof that less is more despite what most people say about KC being "generic"(what they mean is that is diferent from most dominant aesthetics in anime today), being an LHA with aircraft capabilities back then gave her some uniqueness gameplaywise too.
If there is something i learned from art in internet is that for something to be popular doesnt need to be rendered with the same standards of what people today considers to be peak art in manga/anime, just look at Zun's drawn characters, people outside the touhou fandom can make fun of their quality but they are iconic and memorable unlike most gacha games; bad/different art doesn't ruin a good design but good art can not save an objectively bad design.
If Akitsumaru is as popular as she is, is not only due to her design as a whole but also thanks to a fandom that actually does give a shit about a niche characters such as her. Thankfully rarity bias is not a desease that KC would ever suffer from unlike other games with MainCast syndrome and bloated list of actually forgetable low-mid rarity characters.