I don't think the criteria for being tsundere is to be evil.
Chiyo is the super upbeat energetic type, besides being cursed with tuberculosis. Her tantrums and begging basically all she could do at this point lol. She has zero power and skills. Urotaru could eventually be tsundere if he starts having feelings for her be decided to keep being an ass.
Ok,you got me again. When I read your post, I went to wikia and found this:
Tsundere (ツンデレ?, pronounced [tsɯndeɽe]) is a Japanese term for a character development process that describes a person who is initially cold and even hostile towards another person before gradually showing a warmer side over time. The word is derived from the terms tsun tsun (ツンツン?), meaning to turn away in disgust, and dere dere (デレデレ?) meaning to become 'lovey dovey'. Originally found in Japanese bishōjo games, the word is now part of the otaku moe phenomenon, reaching into other media such as maid cafes, anime, manga, novels, and even mass media. The term was made popular in the visual novel Kimi ga Nozomu Eien.
I focused too much on the term "hostile"; from there I understood it as a moral term. But rereading it again, (I'm not good with those terms) I see it applies much more to a character who changes between being cold, irritableor hostile to being warm. Here the tropes def
The Japanese term tsundere refers to a character who "runs hot and cold", alternating between two distinct moods: (aloof or irritable) and (lovestruck).
I'd say, I have being applying it to gratuitous coldness or hostility or huffiness;and I think there's some reasons to do it, and that the "gratuitous" element is esencial in tsunderes. Otherwise, all transformations from cold or hostile to warm should have to be taken as tsundere. But, for example, Fraudrin or Meliodas from SdS, to take common references between us, suffered transformations from hard rude guys to have a soft side. But are they tsunderes? I don't think so, nor I think all transformations can be taken as tsundere's transformations.
Anyway, I thought Chiyo was tsundere because I find her tamtrums a bit overdramatic and in that sense gratuitous and even "cartoonish", a bit beyond the line. Now I don't think all she can do is tamtrums and begging. She's brave, which is interesting since she lacks of powers of figthing skills. To me, that bravery in a powerless character suits much better with a sobern person than with a cartoonish one. But that's just personal preference.
I wouldn't call Uroutaru tsundere. Basically because his coldness and apathy have deep motivations in his long history: they are not gratuitous. (It's like for a tsundere, the warm side is hidding behind the cold side, but it's there from the beggining). In Urotarau's case it's more like Chiyo is going to break the wall of ice with her actions. Now as I said, I think it'd be much more interesting if her actions are not tamtruns but better the brave actions she just did or actions of other type.