[Minoto]

Well, certainly not everyone responds to trauma that way, but some (speaking from personal experience) do.

Here's something else to consider, from within the story itself:

Spoiler for Shouldn't be a spoiler for anyone reading this thread, but just in case:

Remember that Misuzu is a partial / failed reincarnation of Kanna, who (despite her appearance and position) was still very much a child by the standards of winged beings during the events of the Summer arc. It's not unreasonable for Misuzu's nature to reflect that.

That was one of the things that made me like this series so much...even though I spent most of my first viewing just barely understanding what was going on, by the end, it provided a reason and explanation (a very supernatural one, but then, it's obvious fairly early on that there's more involved than just everyday reality) for all the mysteries it presented earlier. The second time I watched it, I caught so many little moments that had just made me go "huh?" the first time, and realized what they meant and how they foreshadowed future events...it was almost like a different show.