11-nin Iru!

They Were 11

The elite Cosmo Academy attracts applicants from every stellar nation in the galaxy. One young hopeful is Tadatos Lane, an orphan esper from Terra. The final stage of the academy's entrance exam is a perilous mission simulation aboard an actual derelict starship. The applicants depart for the ships in groups of ten, but when Tada's crew arrives on the Esperanza, they are horrified to discover that they now number eleven. As the test progresses, things go awry and the atmosphere grows increasingly tense. The crew members begin to suspect sabotage, and Tada appears to be the likely culprit.

(Source: Anime News Network)