I could totally picture it in my head. Chihiro meets Yugami at a diner or a coffee shop of some sort and complain about her love life. Yugami will make some comments about it. After some good banter, they find that their monthly meeting is more fun than the whole dating things.
One thing lead to another, Yugami finally propose (mind you, maybe with the family pressure or some shenanigans, and he will do a stellar job at it - with a twist - once he put his mind to it), to which Chihiro just casually agree "sure".
And then there's the shocks of everyone around "that guy, he could get married!!!?" Everyone will be in total chaos: some will exclaim "of course" upon learning that it's Chihiro, some will tell the bride to be it a bad idea, others who do not know the groom to be well will be curious, etc.
I imagine their dating and married life will be no different from how they are now (kinda remind me of Accept My Fist of Love manga but not quite). They enjoy each other's company (without really knowing it), they help each other become a better person little by little (without being aware of it), they accept each other's good points and flaws (without thinking about it), etc.