Sentinel (formerly known as Pz. Hu-2172) was a robotic dog created by a war hungry country. His original task was to locate and subdue hostile targets as well as guarding several facilities. However, the country was destroyed by rebel forces lead by a one-man army supersoldier and Sentinel hid on a facility holding a 'time-machine' that would allow them to alter history. Unfortunately something went wrong and he was sucked into the spacial-time rift and landed on the Rift Cafe, where he stayed and lived there for quite some time before he was appointed to guard the cafe, thus giving his current name: Sentinel.
As Sentinel was designed to be a war machine from the start, he is sometimes aggresive when threatened and he has no qualms of hurting anybody but his 'masters'. After spending some time in the Rift Cafe, his aggresive personality starts to fade and he becomes friendly to most visitors, except for one man. He now acts more like a well-trained pet dog only being a robot of course. Of all the regular customers of the cafe, he prefers to play with Zombie but always growls when he sees Hoshino.
- Durability: His armored body is designed to absorb heavy damage and protect his integral parts.
- Fast Runner: As he is designed to hunt and subdue targets, he can run to a speed of about 88 mph. If he ever reaches 88 mph, trails of flames are usually seen behind him.
- Sixth Sense: Sentinel has an ability very few robotic dogs have, the Sixth Sense. This ability allows him to be constantly aware of anything around him and thus giving him almost impossible reflexes.
- Strong Jaw: Being a robot, his bite force is 20x stronger than an average dog and can chew through steel and concrete easily.