Hell hath no fury (like a man in green armor)

Highway to Hell

Just outside of the glorified club house, the others of the Peerage simply hangout by the entrance.

Yuuto: Soooo yeah. That guy.

Rossweisse: Just, damn.

Koneko: Yes, we get it!

Issei: I don't like him.

Asia: What do you mean?

Issei: Some Master Chief looking dude pops out of nowhere, kills a whole bunch of stray devils with no trouble what so ever, and Rias just brings him in without a second thought.

Akeno: You don't trust her judgment?

Issei: All I'm saying is that something about this guy just screams impending doo-

The sound of muffled gunfire and magical discharges can be heard. They look up at the schoolhouse and see flashing lights coming from Rias's office. Before anyone could move, a loud explosion resonates from the building along with the sound of wood splintering.

The whole group finally decides to rush in the building to her. As they scale up the building, they make it to Rias's office. What's left of it at least. The door is off its hinges, most of the furniture is destroyed, and there are bullet holes and scorch marks everywhere. Most noticeably is the giant ass hole in the wall leading outside with a bloodied and bruised Rias facing it while clenching her side.

Issei: What happened?!

With the help of Akeno and Yuuto she is led to one of the remaining intact furniture with Asia at her side to heal her.

Rias: He just "grunt" attacked out of nowhere! After my discussion he started shooting at me.

Asia: Why would he do that?

Issei: Oh, I'm gonna kick his ass!

At that moment a frag grenade flies through the wall and clatters on the floor.

Rossweisse: Look out!

Moving quickly, Rossweisse raises a magical barrier around them just as it goes off. The force of the blast however tears through the barrier and flings most of them back in a daze. With most of them disoriented from the blast, Gasper struggles to stand back up. From the hole in the wall Doomguy uses his thruster boots and makes his way through with assault rifle in hand. Being the closest to him, Doomguy casually walks to him as Gasper starts to panic. The marine quickly raises his boot and prepares to stomp the little cross dresser's head in. The last thing he sees are Gasper's eyes flashing red before stomping his foot onto empty carpet.

Confused he looks around and sees that everybody else is gone as well...

What the fuck happened?!

In the halls of the schoolhouse the devils run to the exit. With the use of Gasper's Forbidden Balor View they were able to get enough time to escape.

Rias: Quick thinking Gasper! Good job!

Issei: What the Hell do we do now?

Rias: We get our bearings and come up with a battle strategy!

Koneko checks over her shoulder and sees Doomguy barreling towards them through the halls. She skids to a stop, turns around, and rushes at him.

Rias: Koneko!

Koneko: Just keep running!

Heeding her advice they keep going as she charges at their pursuer.

Koneko: Let's see how tough you are, you son of a bitch!