Episode 52: Pages 52-66 of volume 4 of the Kodansha publication. [source]
Come to think of it, I don't think I've ever seen Akira himself desire those drugs the same way every other numbered esper does. Is Akira perhaps the only one who found a way to live without them?
Also what, surprise incest? I thought Ryu and Kei were siblings, or was that just a lie?