Soul Stone
"There's no problem." The old man said, "Anyways, since you said that will be your last question, I will now proceed with the request that I want to ask of you."
Then the old man shifted the talk to the main topic of this talk
As you might have or not already guessed, this old man is obviously Leviathan if you still haven't realized it yet.
Being a Deity, he has a lot of different skills and abilities, one of those is the transformation skill(Humanoid).
It is a skill that can allow the skill holder to become a humanoid being, to allow them to associate with others. This skill is usually used by non-Humanoid like monsters, high level animals, etc.
That is the reason why a whale, who is very big and can flatten a human, can appear as a human.
The two continued to talk about the things Levi wants to request of Fred.