The signature Chibi style in which Numenoko likes to draw Komeiji Koishi, Flandre Scarlet, and a few others. They also offer commissions of any character in this style, and have drawn commissions of everyone from other Touhou characters to Karl Franz from Warhammer Fantasy (post #4193293).
"Tan tan pou" is a nonce romanization of たんたんぷぅ, which in formal romaji would be <i>tan tan puu</i>.