Chief is having a bit of depression about Cal's Demise.

(Flashback)

O'Brien: Chief, I hate to say this but Cal is gone. I'm sorry, Master Chief, sir.

This broke Master Chief's heart that she's gone forever.

Master Chief: Thank you, Sir. I need some to be alone.

He walked away from them as he secretly his tear rolling down his cheeks inside his helmet.

Cortez: What's wrong with him?

(End of Flashback)

He took off his helmet looking at the view of the Earth shedding his tears. He did not know when O'Brien and the gang watched him. Seryu uses her magic.

Master Chief (thoughts): I was about to tell her but now she's gone. I have feelings for her and I love her. Why did she leave me?

They realized that Chief loved Cal so much.

Akame: Tatsumi.

He put on his helmet and went to the training room as they follow him. When they enter the training room. Master Chief was punching a wooden stick but much in their horror, he's punching bleeding as his hands were covered in blood.

Akame: Tatsumi, stop!

He kept doing it as his hands were bleeding much worse.

Akame: Stop!

He stopped and turned around to see Akame as he breathes heavily.

Akame: Stop, just for today, Don't be Spartan, Don't be a mask.

She took his helmet off revealing Tatsumi shedding his tears as he closed his eyes in sadness.

Akame: it's okay, let it out, just for tonight. Let yourself fall apart.

He finally breakdown his emotions as he kept sobbing.

Akame: I promised I'll put you back together.

O'Brien felt sympathy for Chief that he lost Cal Forever after that later, He finally calm down

Akame: Tomorrow we have another day.
Master Chief: what is it?
Akame: We're heading to Requiem.

The Next Morning

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After they went into the requiem. Master Chief fought the Covenant Forces and proceed to Forerunner Structure when he entered it, he saw someone in the light as he aims with his rifle.

Master Chief: Who are you?
???: Don't you recognize me, John?

he couldn't believe it in his eyes: It was Cal who is now resurrected.

Master Chief: Cal is that-
Cal: Yes, Chief it's me.

She saluted at him but he rushed and hugged her.

Master Chief: I missed you.
Cal: I missed you too.

Then she took off his helmet and kisses him.

Master Chief: I love you.
Cal: I love you too.

Then they regrouped as they felt happy to see her again as the battle finally died out.

Master Chief: How?
Cal: It's a long story.

Then Librarian appeared in front of them.

Librarian: I founded her and treated her from her injuries.
Master Chief: Thank you.
Cal: The Librarian told me that you have some depression about my demise and how much you love me. As I said, I won't leave you and I'll be with you forever.

He couldn't help but smile.

Master Chief: it's good to have you back, Cal.
Cal: Yeah.
O'Brien: Welcome back, Cal & I wanna say... Thank you for saving me.
Cal: you're welcome.

Cal has finally reunited with her friends and his fiance, Chief.