I don't think the author gave much thought about asexuals or aromantics. they just wanted to write a "funny" story and just used something as an object for this purpose. it is somehow disturbing. other than that, some person who can't fall in love (FL) to be able to enjoy love stories is also confusing.
and like mentioned before, i also wish this was somewhat a dormmate or roommate thingy and something shit serious like marriage wasn't the case. well, in japan one just has to fill a paper to get married. maybe that is why they can take all these as a joke.