Reika Yamamoto 山本 麗華 (Yamamoto Reika)
Reika is one of Alice's two constant companions. The official site describes her as a classmate who is always with Alice and Juri, steady and cool in manner, who likes to have things made clear and often presses Lain. Konaka explained that Reika, Juri and Alice were names he reused from his earlier cyber fiction: they go back to a 1994 live-action school ghost-story episode and to the game Alice in Cyberland, and he reused Reika and Juri again in Digimon Tamers because, as he put it, he likes these characters even as their faces and ages change. Chiharu Tezuka voices her in Japanese; the English credit is often given as Lenore Zann, whom ANN lists only as "Lain's friend 1" (credited Lenore Zann on Layers 01 to 04 and, per ANN's alias list, Zan on 05 to 13), so the match to Reika is unconfirmed?.
More (spoilers)
When the rumor about Alice spreads in Layer 08, Reika and Juri stare at Lain as if she might be to blame. By Layer 12 they are chatting with a strangely cheerful Lain while Alice watches uneasily. After the reset, Reika and Juri are walking to school with Alice as before, planning a night at Cyberia, with no memory of Lain at all.
Sources: en.wikipedia.org archived · ja.wikipedia.org archived · lawmune.net · lawmune.net · lain.wiki · lain.wiki