Sempai-Kohai

The concepts of sempai ("senior" or "upperclassman"; pronounced "sempai") and kouhai ("junior" or "underclassman") permeate Japanese society. They're most usually encountered in Anime in situations set in school, but the system also applies after graduation in the workplace. Older students (or workers with greater seniority) are known as sempai, and junior students/workers (or kouhai) are required to defer to them, and address them with the honorific -sempai. In return, the sempai is obligated to look out for, and protect, the kouhai.

While similar concepts are widespread in Eastern Asia (for example, in Korea the concept is known as sunbae and hoobae), none of them have it as entrenched within the social structure as the Japanese.