That depends on which one! But...hrmmmm...arrrrgh... Okay have four, depending on which one you chose!

Ryu - A friendly spar leads to flirtation, which may or may not embarrass the hell out of one of them.
Charlie - The last night before the mission to destroy Shadaloo.
Vega - A seductive showdown, with increasing scarcity of clothing. (I'm so bad.)
M. Bison - A failed mission results in Chun-Li waking up somewhere she'd really rather not be, ever.