Koe ga Hibiite Yuu to Nari

Otose is a rookie voice actor with a childhood dream in his heart. While working part-time, he is suddenly summoned by his agency and learns that his first job will be voicing the lead role in a BLCD, as the original author wants to hire a rookie voice actor. To prepare for his debut, Otose takes individual lessons, only to discover that his instructor is Sakai, a legendary voice actor who played the lead in his favorite hero anime before retiring five years ago. Overwhelmed with excitement at Sakai's intense training and demonstrations, Otose begins to develop feelings that go beyond admiration. However, he learns that Sakai is HIV positive, which was the reason for his retirement from voice acting...

(Source: Shufu no Tomosha, translated)