Stryker followed the scent of Ruby from where she landed. He then heard gunfire and screaming. He knew it was Yang and that she could take care of herself. He was more concerned about Ruby. He ran off to find her. He followed her scent while killing Grimm. He saw Ruby with her cape stuck on a feather. What's worse was that she was about to be attacked by a giant Deathstalker. Stryker ran off to save Ruby while letting out a loud roar.
Ruby was trying to get her cape free, but it was useless. She saw the Deathstalker get closer to her while her sister tried to get to her through some feathers. Ruby closed her eyes and waited for the blow, but she opened them when she heard a familiar roar fill the air.
She turned and saw Stryker bite off the tail of the Deathstalker. Yang had a calm and happy expression on her face as she saw Indominus Rex. She turned around and saw everyone else's expressions. Blake's face had practically screamed one word: predator. The rest of the students were just slack jawed and bug eyed while Weiss said what was on everyone's mind, "WHAT ON REMNANT IS THAT!?"
"That's Stryker," replied Ruby.
She brought up Stryker earlier to Weiss by accident, but Weiss didn't believe it. But now the beast was right in front of her.
"THAT'S STRYKER!?" she cried as she watched Stryker clamp his jaws on the Deathstalker and crush the armor like paper.
After successfully killing the Grimm, he let out a triumphant roar and ran over to his girls. He did a quick inspection to see if Yang was okay, and she was not to his surprise, then he did a more personal inspection on Ruby, sniffing her all over and tickling her.
"It's okay Stryker," said Ruby, "I'm fine."
Just then a bird grim called a Nevermore came and circled back and a large Ursa appeared.
Stryker roared at the Ursa and got it's attention. The Ursa was as big as Stryker and they both roared at each other.
The Ursa clawed at Stryker, but the Indominus was able to grab it's leg and flip it over. The Ursa chomped down on Stryker's arm, while he clamped his jaws on it's neck. After killing the Ursa, Stryker then ran off to find his girls and the others. He was so preoccupied about Ruby, he didn't notice that he was watched in the trees by a creature very similar to him.
After initiation, the now formed Team RWBY were heading off to their dorm, when they heard a little roar. They turned to see Stryker appear behind a corner and walking towards them. He then got on his side as Ruby and Yang scratched his belly and his head.
"So you guys have a giant killing machine as a pet?" asked Weiss.
Stryker then whipped her head with his tail.
"We don't use the P word," replied Ruby, "He almost mauled someone for calling him that."
"Who did he maul?" asked Blake.
"Our Uncle Qrow. He ALMOST mauled him. Stryker took his drink and our uncle called him the P word."
"He truly is a remarkable creature."
They all turned to see Professor Ozpin walking up to them.
"He's the only creature of his kind," said Yang.
"Can he stay?" asked Ruby.
"Will he be a problem?" asked Ozpin.
"If no one threatens him or Ruby," said Yang, "then he won't kill anyone."
Ozpin thought for a moment, before saying, "Alright, he can stay. I am rather curious as to what he can do."
Ruby and Yang cheered and Stryker let out a happy roar. Look out Beacon, the Indominus Rex has come to stay!