The artist is Korean, and Tsuyu's name is 츠유 in Korean (romanized as Cheu-yu). Korean lacks the /ts/ sound, so it is approximated by /tɕ/ (ch), very similar to the corresponding sound written ch in romanized Japanese as in the names Chiaki and Chinatsu. As such, tsundere is actually cheundere in Korean. Contrast that with English, where loanwords/names with word-initial /ts/ are typically pronounced using /s/ or /z/ with the /t/ dropped (e.g. tsunami → /sunami/ and tsar → /zar/).
