Tracker

"Stubborn little things. I thought they were all dead, but I see at least one survived."

The Tracker (ついせきしゃ Pursuer) is an enigmatic mask-like entity that Seto encounters many times during his adventures. It regards Seto as a nuisance and does not hesitate to attack.

Its speech proves it may not be as supernatural as it seems. It is not in fact a ghost, it is actually a self-aware AI like Shin, even revealing this later on with the line "When we were conceived the age of man ended".

Story
The Tracker first engages Seto in the empty Observatory that served as his former home. Though nothing about the Tracker or the past is known at this point, it refers to Seto and humans in general as "stubborn little things" and expresses surprise at any survivors, alluding to some connection with the apocalypse. Seto quickly dispatches of the Tracker before beginning his journey.

The Tracker appears again in Lunar Hill Fun Land. It surprises Seto as he exits the underground tunnels in pursuit of Crow. It offers no words this time, and simply attacks. Seto defeats the Tracker and continues on his way, only to encounter it again in the Kurato Kankou Hotel. While originally following Sai's voice, Seto is led to the hotel chapel, only to be ambushed again by the Tracker. It attacks more aggressively this time around and, after being defeated, drops the Key to Room 301.

In Battle
In its first confrontation with Seto, the Tracker does not attack and merely serves as a tutorial to introduce the combat system. From Lunar Hill Fun Land and onward, the Tracker begins to attack Seto and becoming progressively more aggressive at each encounter.

The Tracker has two distinct attacks. The first consists of two short and light strikes. The second is a downward smash of its mask that is slower but delivers more damage. While these attacks themselves are not overwhelming, the Tracker has a tendency to disappear and appear behind Seto before attacking. When not attacking it floats away from Seto, circles him, or simply vanishes in an attempt to strike from behind.

Trivia

 * The "Tracker" is an unconfirmed name, as no official English counterpart has been given to the Japanese name.
 * He could be based on the Phanto a Super mario bros 2 enemie who's also a flying mask.