The plot is incredibly straightforward and cliche- humans at war with demons and a person is summoned to help deal with the problem, albeit, not in humanity's favor.
Akari as a main character is a pretty one dimensional character whose personality and role is the story can be summed up as 'Cute emotional girl who wants to protect her friends but is weak.'
However, the main pull of the manga isn't the story itself nor the characters or literally much of anything else that most people would consume media for.
Its stupid and its fun. This manga is stupid and you're not suppose to put too much thought into it, its like overexplaining a joke. The whole punchline of the show is the main character becoming pregnant through every other means except sex itself and rapidly pumping out cutely chaotic demon babies. Its not exactly high class. But its something you can mindlessly watch while enjoying the visuals of a cute girl with equally cute babies ending up in absurd scenarios. Who, of course, end up getting saved by some hot guys or the babies themselves stepping up to protect their mama.
There is plot and there are characters, but they're both just there to help shove down the cuteness and strange comedy. They're not the main focus here. There is some potential of both becoming more relevent thanks to some light world building and foreshadowing - but I doubt it.
To summarize, don't overthink it.