Well, it's summer, it's hot, Lee and Amber love beaches and ice, the sand is too hot for Amber's feet, Lee wants to be gentle and Amber loves to tease Lee... xP
This is about three years after the ninja-war what means Lee should be about 21 years old here. Amber is his... training partner from the Batman Universe...?! Well, they met while Lee came with Curse to the House of Secrets for two years(belongs to DC Comics, the dimension where Curse comes from.) Lee wants to learn more martial arts from Catwoman and Bane (by the way, he is Curse's brother). Amber is the student of Selina (catwoman) and was born as an kitten. You can read more about her here: [link]
She has also no abdominal muscles (like a cat). That's why she's usually wearing a corset-like armor that saves he in fights.
Selina wants Amber to become a hero at Batman's site, because she isn't able to be a good one for longer time (she's a kleptomaniac and canÄt stop stealing fancy things)
Amber wears a collar because... she likes it... and Lee because Amber gave it him and he accidently promised to keep it on, as long as he loves her. Cute, huh?
Rock Lee © Masashi Kishimoto
Amber, Artwork © 94Catgirl