What do you think of the beginning of my story?

I think it does sound very good so far. I would explain WHY they were known as Rena and Leiko. You also might want to condense their physical description- maybe something like,"...but now she had straight, kelp green hair that stopped just below her shoulders.'Leiko' used to have pink, wavy hair and hazel-yellow eyes, but now her hair was a lighter shade of green than her sister's." Other than that, sounds good so far.