Because Shen wiggles his butt when he walks, he becomes Ender’s first friend at Battle School. That is, Bernard makes fun of Shen and Ender gets back at Bernard – so that makes Shen and Ender BFFs. Shen is also one of the people who Ender practices with. In fact, when the older boys attack the practice session, it’s largely because Shen was throwing their insults back at them. He kind of disappears for a while, though he ends up at the end as a squadron leader under Ender. But his most important role is probably as Ender’s first friend.