Rek'sai is part elite confirmed.

https://support.riotgames.com/hc/en-us/article_attachments/202612284/Pool_Party_RekSai.jpg

Notice Reksai's mouth^

http://i.imgur.com/4iUBqz2.png

Notice the Elites mouth.

Confirmed Reksais father had kinky sex with a dolphin and rek'sai was born