This manga is such a Kodama-sensei story. This is the formula her manga always use:
1. Write an interesting premise for an adult romance - two former classmates who took very different life paths but end up working at the same place
2. Explore that premise in a fairly interesting way - have an ironic reversal wherein one girl was mean to the other, but now that they're co-workers the previously bullied girl is the boss, frustrating the bully. But unbeknownst to the bully, boss girl was always in love with bully, and doesn't know how to handle their new dynamic.
3. Ruin the story via creepy sex stuff - making boss girl sexually harass and then assault bully girl. I know bully girl does eventually "like" boss girl, but its in a worst way possible. Like, Miyata harasses Nagao, Nagao says no, Miyata harasses her more, Nagao says no again, Miyata straight up starts trying to fuck Nagao, Nagao goes "who could resist?" and starts to enjoy it. The manga is essentially saying "If she says no, don't worry! Keep going and she'll eventually want it!" I hate it.
So many of Kodama's stories have this pattern of good premise spoiled by creepy sex stuff. The type of creepy sex stuff changes; sometimes its incest, sometimes its sexual assault, sometimes its cheating on a partner. But its consistently there. The only reason I keep reading her work is that sometimes the good aspects of her stories are strong enough that I can tolerate the shitty parts, e.g. "Umineko-sou days" or "I Decided to Fake a Marraige with My Junior to Shut My Parents Up". Unfortunately this story was not good enough to ignore the bad aspects.
Oh, and I guess I should specify that the creepy sex stuff doesn't bother me by itself; there are plenty of ecchi/hentai manga that do way worse things, and I just don't read those. What bothers me is the wasted opportunity to do something better with the premise. I realize with a 15 page one-shot you have to move quickly, but there are other things you could do. Maybe Miyata goes to help Nagao after work, and they start up a conversation about high school that leads to romance. Maybe Nagao complains that Miyata is bullying her as revenge, and that leads to an argument in which Miyata confesses. There are loads of ways you could make this work without sexual assault. Admittedly those routes still have the problem of a boss/employee power dynamic, but if the sexual elements were more equal, I think it would make the story feel morally grey instead of completely amoral.