I don't think that's Seiga. Personality seems more like Nazrin to me + the round part is a darker color than her hair, so it might be an ear (Nazrin's ear tips are darker than her hair).
Plenty of characters and people within and without Touhou (including in reality) utilize "ze" (or in this case "zo"), as an indicator of a style of speech. It does not mean "I tell ya".
Wow, I hadn't noticed how bad "I tell ya" usage had gotten. Looking through the list of posts it's been used on, most of the time it doesn't even make sense to be there. Just seems like a really lazy way to address a "rough" speaking style, instead of actually writing "rough" dialogue.
It's fine! I don't mind!Whew!BMP-BMP!GH-!!AH!!What a lovely bath that was!BTSSTI... I HAVE A NOSEBLEED!!Come back out when you've put proper clothes on! This ain't your house!