Who becomes Ender's first friend? Under what circumstances?

Shen is part of Ender's launch group. He becomes Ender's first friend at Battle School, when Ender defends him from Bernard's teasing. After Bernard points out to everybody that Shen's butt wiggles when he walks, Ender finds a way to send a message to the whole launch group saying, "Cover your butt. Bernard is watching"--signed "God." Even though Ender never owns up to sending the message, he is the first to point it out to Shen, so Shen understands that Ender is his ally. Shen is later one of Ender's squad leaders during the bugger battles at Command School.