I think you may want to give a few reasons to why the MC bears with it from the start. I mean right now the best i can think of is that he is really stoic in nature and thinks she may have answers, maybe emphasis on the latter a bit more. I mean the dude is an orphan, so maybe he enjoys having some presence around him too, even as obnoxious as this girl can be.
I may be wrong, but i thought tsundere acted in a distant or violent way only toward their love interrest, not toward random strangers. To me Mikiko is more a violent bitch trying to avenge her parents death more than a shy girl hiding her feeling under a layer of icy behavior or agressivity. I did get hints about you going this way though, all the more with the end of the current version. Not that there is anything wrong with a PTSD riddled girl.
English is fine, for the most part.