They Were Eleven!

With the discovery of warp-navigation, the inhabitants of Terra-Earth have expanded into space for several centuries. Numerous planet nations have emerged as a result. In the process of expansion, humans met inhabitants of other systems, such as Sava and Seguru. After many cycles of war and peace, the various planet nations signed the Interstellar Alliance Treaty. At long last, peaceful coexistance in space has been achieved. Cosmo Academy. Established 120 years ago to usher in the new era. This elite institution contains the finest space science facilities and exists to educate the leaders of the future. The graduates are promised elite positions in their society. From Terra, Sava, Seguru, and other stellar nations have gathered aspiring applicants.... The applicants leave for their final test in groups of ten. But when Tada's group arrives on the Esperanza, they are horrified to discover an eleventh member. Which of them is the eleventh member, and what is his purpose?