@yotsuba428 i think we're all missing the fact that there's two different types of tsunderes - classic and modern.
classic tsundere describes permanent behavior; ie initially cold or hostile to gradually warming over time (albeit nino is more instantaneous)
modern tsundere is more temporary; as in switching between hostile and lovestruck, kind of personality swings (i guess itsuki, but i feel like throughout the entire manga, itsuki and fuutarou's relationship has been one of admiration for each other's work ethic than anything actually romantic, hence what i see as a lack of true deredere. she gets embarrassed a lot, sure, but out of being lovestruck? - not entirely sold on that)
classic tsundere describes permanent behavior; ie initially cold or hostile to gradually warming over time (albeit nino is more instantaneous)
modern tsundere is more temporary; as in switching between hostile and lovestruck, kind of personality swings (i guess itsuki, but i feel like throughout the entire manga, itsuki and fuutarou's relationship has been one of admiration for each other's work ethic than anything actually romantic, hence what i see as a lack of true deredere. she gets embarrassed a lot, sure, but out of being lovestruck? - not entirely sold on that)