The Lost Thing

I think lost thing is things we used to have when we were young.
Story begins when boy found the lost thing on the beach. Because everyone else didn't notice about it, he began to look for the place lost thing can fit. And at the end, they found a place where many strange creatures like lost thing live.

In the video, lost thing is representing our younger days and our hopes or dreams we used to have. May be everyone else couldn't see it because they already gave up their dreams. My opinion is kind of similar to Yusuke, may be :)