As Plutia neared him, Ben felt something off, so his hand neared his Omnitrix. This Plutia's mana was... something.
Though, the fact that no one knew him confirms one of few things - A, he was away from Earth and on a planet that had not heard of him or would only recognise him via his Omnitrix, B, he was in another universe where he did not exist. The latter definitely happened before, when he met one of his allies - Rex Salazar, the 'robot boy' as Ben calls him.
The best way to confirm this was to introduce himself.
"I'm Ben Tennyson. Just call me Ben," he replies humbly, "good to meet you, Plutia, and... uh... the rest of you. Whatever your names are."
"Ah~ If I'm not mistaken, I believe that watch is known as the Omnitrix? Capable of transforming the wielder into numerous different creatures, correct?"
@Crow
"Is that a share crystal?" asked Neptune, pointing to the piece of magicite with a curious look in her eyes. "Nah. It couldn't be. I can tell, you're not from my world, so you wouldn't have share power. So what is it then? Some kind of magic crystal? Can you rub it and look into weird and far off worlds with it? Sorry. Just being curious here. After all, getting to know new friends is important and everything. Something tells me it's more like a game disk than a share crystal anyways. Something you equip to augment your abilities and the like."
"Share crystal?.. Oh~" Terra then realised what she was talking about as she pointed towards her necklace. "Oh. This is Magicite.. It's a physical crystal that houses a living being known as an Esper.. Which are strong beings that naturally pulsate and know Magic. This one is a special one to me which I hold dear to my heart.. Let me introduce you to him.." She then closed her eyes and held onto the crystal gently and a magical creature had spawned forth in front of her:

"Daughter? Is something the matter?" "Hi Father.. I'm just introducing you to my new friend.. Her name's Neptune." "I see. Well then, "Neptune" My name is Maduin. I'm Terra's Esper Father. Do help me keep an eye on my girl, would you? While she possesses incredible magic power from my heritage, she can still die all the same. If you have any questions about me or my kind, I will be more than happy to educate you if you desire it."
@Snowtwo