In mission mode, he will appear during some missions and will always appear with Miyako Sudo's ghost; he has a high amount of health, but as with Miyako, he's the weakest ghost and will remove only a small amount of Mio's health.
He can make an appearance in the main game if the player has completed the bloody ring sidequest, by collecting the notes on the Osaka House in Chapter Two and examining the respective locations:
Check the base of statues to the left by the lone pinwheel, in the stairs leading to the Kureha Shrine. This is Village Report 1.
Following the sidequest, in Chapter Four, in the storeroom of Kurosawa House, Masumi's ghost will appear (non-hostile), and after taking a photo of it, the Bloody Ring will appear on the ground.
In Chapter Five, upon entering the back room of Osaka House, a cutscene will play showing the fates of Miyako and Masumi. Mio then picks up Masumi's bloody memo and a Spirit Stone called Sard. Then the ghosts of Miyako and Masumi will attack Mio.
After defeating the ghosts, Mio picks up another file, Miyako's End, which explains that Masumi was killed by the Kusabi.