Stories like this are rare.
Despite the cutesy art style... they are unmistakably adults... they shagged XD.
But jokes aside, what is truly impressive is... the lack of juvenile awkwardness, don't mistake for the lack of normal awkwardness, what I mean is the almost infantile way adults act in mangas, like they are overgrown children that can't talk with each other without blushing a storm.
Such things have their place, even in real life... but adults, not matter what the issues they have, are able to communicate in ways children don't.
The author of this manga understands this. Despite Takaharo being very centered and assured, he has his little quirks and insecurities, he was hurt by the sudden breakup, but he kept going, living his life, and despite Kyou being almost the quintessential cutesy love interest, she is a single mother who dealt with all the challenges that come with the territory.
Both of them are unmistakably adults.