That looks like a head wound. And Flandre is no pushover. Yuuka likely had a challenge, and enjoyed the rarity of such an occasion.
having said that, I wanna see more Yuuka vs(x) Flandre. Much more~~~
Haha... I never thought she would have that much power...*Shiver*Mmmm...Are you awake?Yes, it's me, Sakuya. I was looking for you.Now... shall we go back home?'though...That was really fun...Good grief... If I wasn't there you would've really been in danger....Saku...ya?