The official Frieren: Beyond Journey’s End website confirms that Yuichi Nakamura will be the voice actor for Sein in episode 13. New artwork for the character was also revealed ahead of the episode’s premiere.
After much anticipation, Frieren: Beyond Journey’s End premiered on September 29 with a lengthy two-hour special. A total of 28 episodes will be released in two cours, and the anime is about to reach its halfway point in just a few weeks. Before the release of episode 13, the staff for Frieren: Beyond Journey’s End shared more insight about Sein, the magical priest.
Sein in the Frieren: Beyond Journey’s End Anime (UPDATED)
Sein is a priest that uses advanced healing magic, but he engages in activities that aren’t as holy, such as gambling and excessive drinking. In Frieren: Beyond Journey’s End episode 13, Frieren and her crew will run into Sein, and this character may have a particular role to play going forward. Once more, Yuichi Nakamura is the voice actor for Sein.
Check out the character artwork and actor portrait below:

Update: The official website also confirms Daisuke Hirakawa will play Sein’s older brother in the anime.

Watch the trailer below.
New Frieren: Beyond Journey’s End episodes release on Fridays starting at 9:00 p.m. JST via Nippon Television (NTV) and streaming services in Japan. Fans around the world may watch the Frieren: Beyond Journey’s End anime on Crunchyroll as it airs in Japan.
Lastly, here’s an overview of the anime series via Crunchyroll.
The mage Frieren defeated the Demon King alongside the hero Himmel’s party after a 10-year quest. Peace was restored to the kingdom. Because she is an elf, she is able to live over a thousand years. She promises Himmel and the others that she will be back to see them and then sets out on a journey by herself. Fifty years later, Frieren goes to visit Himmel and the others. She remained unchanged, but Himmel and the others have aged and only a little of their lives remain. Later, she witnesses Himmel’s death. Frieren is pained by her desire to have spent more time getting to know people. With that regret in her heart, she then goes on a journey to do just that. On her journey, she meets many people and many events await her.