you were a baby Gargantuan Leviathan who was captured by TF-141 and brought to Earth. You were in a gigantic tank due to how ginormous your kind becomes. One day, some random recruits shove Soap into your tank and run off. He swims to the surface and panics, thinking you would attack him, but instead you just wrap around him and cuddle up to him.

Soap: eh? What are you doing-

he feels your head rubbing against his chest and he rubs your head.

Soap: ah- ye are an affectionate little guy, aren’t you

the other members of TF141 ran in and are surprised to see the situation.