This dissertation is comprised of ethnographic research that has revealed the mediatized nature of seiyū, or Japanese voice actors and actresses. The concept of seiyū has undergone a drastic change throughout the history of Japanese popular culture. Around 2020, seiyū emerged as prominent public figures who are admired and beloved by the masses. This dissertation investigated the new skill requirements for seiyū as a result of role shifts and an expansion of their range of activities, as well as how aspiring seiyū acquire those skills through training. This research is based on two years of fieldwork in Tokyo (from April 2018 to March 2020), focusing especially on participant observation at a school for seiyū for an academic year (from April 2019 to March 2020) and in-depth interviews. The findings demonstrate that young aspiring seiyū are required to develop their skills in three main spheres. First of all, as actors and public speakers, they are trained to develop specialized bodies to manage the high standards of the Japanese entertainment industry in vocalizations, pronunciations, and acting. Secondly, as celebrities whose popularity significantly affects their careers, seiyū need skills in self-branding and marketing. It is crucial for seiyū to understand and utilize metasemiotic frameworks in the Japanese entertainment market in order to gain fans and enhance their career opportunities. Thirdly, as workers, seiyū are required to have specific social traits, including being reliable, responsible, hard-working, considerate, and passionate. Students are expected to be familiar with the culture and rules of the Japanese workplace, especially in the entertainment industry. Aspiring seiyū develop their skills in these areas through their training in the school for seiyū. By achieving a certain level of proficiency in those skills, they are considered to be ready to work in the market; in other words, they acquire the "seiyū persona."