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).

Commentary bump, confirming that's Nazrin. Pesogiso, referenced here, likes Nazrin enough that she's his avatar, and he draws her with that hairstyle.

Looks like Asn got a peek at Ao's Banana, and he enjoyed it more than he thought he would.

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".
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

Swifft said:

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.