Plenty of characters and people within and without Touhou (including in reality) utilize "ze", as an indicator of a style of speech. It does not mean "I tell ya". Your interpretation is *without* basis, don't mistranslate. In this case the "da ze" is meant in its memetic sense, thus "translating" it serves no real purpose. In any case, it doesn't "mean" anything.
Refer to:
https://www.lingualift.com/blog/japanese-emphatic-particles/
https://en.wiktionary.org/wiki/%E3%81%9C#Particle
https://www.nihongomaster.com/dictionary/entry/96937/ze-zo

I literally don't care. I'll translate my own uploads the way I like.