I assume the artist is drawing inspiration from Japanese for the text.
Just to let you know, the writing on the side of the backpack is 十二九, 10-2-9. If the artist wanted to say 29, they would have put it as 二十九. Unless of course this is Chinese, and that is how they do it, idk. The one on the sleeve is 月, which means moon, but can be a shortened version of Monday, which is written as 月曜日 in full.