Seiyuu is the Japanese term for a voice actor or actress. In anime it names the performers behind the characters, whose casting is a credited production role and whose performances are a defining part of many series.
Seiyuu are working actors in a large industry, cast through auditions and agencies, often voicing several roles a season alongside radio, narration, games, and the occasional music release. A single performance can define a character for decades, which is why casting announcements are news and why a famous role follows its performer through their whole career.
The credit is a production fact of the work, and this site treats it exactly that way: who voices a character is quizzable knowledge, the same category as who composed a score. The person is not. A performer's private life, health, relationships, and disputes are never content here, in either the Japanese or the dub industry.
International fans meet seiyuu mainly through the work itself and through sanctioned channels like credited interviews and event appearances. That boundary, celebrate the performance and leave the person alone, is the standing rule of this vertical, and it is written into the blocklist rather than left to taste. The profession's history is long enough to have legends of its own, performers whose careers span half a century and whose voices anchor several eras of the medium at once.
In use"The programme credits list each character beside their seiyuu, the same way a film lists its cast."