Master Chief fought the Covenant off with friends' help.

Akame: Well that's the last of them

Then Covenant Forces arrived.

Mine: You gotta be kidding me!

Then Covenant Forces got killed by Freelancers Grif and Simmons.

Master Chief: Grif, Simmons?
Grif: Chief, my Man.
Simmons: It's good to see you again, Chief.
Master Chief: Everyone, Meet Grif and Simmons.

After Introduction

Akame: So you knew about him.
Grif: Yep
Master Chief: What happened back there?
Simmons: Well...

(Flashbacks)

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(Watch it)

(End of Flashback)

Grif: That's how it happened
Simmons: Caboose is such as a child.

Master Chief sighs

Akame: What's the matter Tatsumi.
Master Chief: Caboose is having some trouble sometimes.
Mine: So, He's an idiot.
Simmons: Let's get to move on, shall we?
Master Chief: Sure.

They went to their base.