My twin and I traveled dimensions. Of those, I know there were versions of individuals with different lives and circumstances. We didn't have the time to get too familiar with people, but even so...

[ Subaru can't say they had a particular word for it, only that they'd seen enough that he can imagine what Jade means. He'd not exactly known the concept in his own world, but they did know of Dimensional Witch. She was how they'd been able to evade a certain hunter for so long.

From a different angle, his home might be a dream to someone else. They might think it doesn't exist, or is somehow less real than their own. The more he turns the thought about, the more he thinks it's a great weight of responsibility placed upon them here. ]

A sea though... It's an interesting image.