1) What’s the maximum amount of time your character can sit still with nothing to do? fucking zero seconds

maybe like three.

very much a taps pen jiggles leg chews on someyhing type of person on top of spending every waking moment like "I could be working on my projects right now"

2) How easy is it for your character to laugh? not very hard, but she will legitimately only laugh if something strikes her funny bone

so she never laughs out of nervousness/just to be polite and there are a lot of kinds of jokes and comedy she just doesn't really get. so she comes off as kind of a humorless person. but then she will completely lose it at a person farting on a dog

3) How do they put themselves to bed at night (reading, singing, thinking?) 1. literally just blacking out from exhaustion at her desk

2. on the rare occasion she actually thinks "I'm tired so I should go to bed" and gets herself into bed she'll wear an eye mask

I shouldn't have numbered these actually she does take a lot of naps in miscellaneous locations

this answer is also dependent on her point in life. while she was active as a surgeon she napped a lot to make sure she was rested, when she was fully withdrawn from society to work on her necromancy she did not bother with sleep until it came for her

4) How easy is it to earn their trust? very. Hifumi just assumes everyone tells the truth by default and also has no qualms about sharing information with or relying on help from a person she met five minutes ago

5) How easy is it to earn their mistrust? if you say you will do something and then don't, or do something else instead, and you can't explain your reasons to her in a way that satisfies her, and it happens 2+ times

then she will think you are baffling and/or incompetent as a person and just think you can't be relied on to do anything right