Kaishain: Aihara Sou no Naishogoto
Sou Aihara is a plain and unobtrusive company employee. However, he is actually a cosplayer āiā who enjoys uploading his cross-dressing on social media. Recently, he has been finding it difficult to jerk off without cross-dressing and using his ass. One day, a handsome man with a fresh, puppy-like appearance, Iriya, joins Aihara's company. Aihara begins to have a desire to be embraced by Iriya, who is a perfect match for his taste, but he tries to suppress it in his fantasy because he does not want his identity to be known. However, Iriya is a big fan of āiā, and when he finds out that Aihara is āiā, he confesses his feelings for him...!
(Source: Kaiohsha, translated)
Note: Includes an extra.