Steins;Gate Episode 6 - Butterfly Effect's Divergence

Dubbing the messages they send to the past as "D-Mails", the group conducts further experiments, deducing the rules and limitations of sending D-Mails. They learn what time they can send messages, how much data can be sent, and how far they can send them back. The next day, Moeka shows up at the lab to see the IBN 5100 and seeks to borrow it from Rintaro. After failing to hide the nature of their experiments from her, Rintaro ends up making Moeka his fifth lab member.