My favorite girl so far. I don't think I would even classify her as much as a hardcore tsundere, as most seem to be doing. So far, all her behavior which could be considered tsun-tsun towards Ichika has had some sort of reason or justification behind it, and she doesn't seem to act tsun-tsun for the hell of it like most tsundere. Could she still be considered tsundere, yes, but I personally don't see it as her defining trait by any measure.
Overall she seems dere-dere when spending time in private with Ichika, with her tsun-tsun side being more targeted towards the other girls.
Quick overview of Houki's actions:
Spoiler for Episode 1:
Class introduction: Houki giving off a interested, shy, please don't make a scene associating with me while you're the center of attention, attitude. Overall it felt like she was expecting him to follow up with something when he brought up her recent kendo tournament win (since she got really embarrassed), but was surprised/relieved when he said something different/unexpected? Later in the episode he conveniently says he has forgotten much of what happened around the last time they were doing kendo (6 years ago), so it seems possible they had some sort of special kendo-tournament related memory in the past.
Break time: Houki takes the initiative to bring Ichika outside, away from prying eyes. Embarrassed, uneasy, shy attitude and pleased he remembered her.
After class at room: Walk's out in a bath towel. Shocked, embarrassed yet surprisingly comfortable. Only became upset when Ichika killed the mood by saying the wrong thing at the wrong time. That finally snapped her out of it and put her on the defensive from impure thoughts, promptly kicking Ichika out of the room so she could dress in private.
After Ichika re-enters room: Embarrassed, shy once again and becomes agitated only when Ichika says idiotic and perverted things.
Breakfast: A standoffish attitude towards Ichika, and still a bit taken aback about the unexpected turn of events the previous night.
Back in class: Once the dual for class rep has was agreed upon, Houki looks like she is concerned for Ichika at the very end of the episode.