Yuugo

Yugo was born in 2017, and he was sent to the Glory Bell orphanage a year later, growing up alongside Lucas, Dina, and several other children.

Around thirteen years ago, Yugo escaped from Glory Bell together with several other orphans. They then took shelter in an underground Shelter where they started a new life. He then found a letter in the shelter, that stated that Yugo and the other children need to go to Goldy Pond where the writer of the letter, William Minerva, left something ''more than just living in the shelter'' behind for them.

The children went on multiple long journeys going through big forests were they encountered Wild Demons and other dangerous threats which meant the end for several of his friends but the man and some others still managed to get to Goldy Pond were they encountered poachers who hunt children for fun in Goldy Pond.
There, the demons seemingly murdered all his friends and Yugo just managed to escape, after which he returned to the shelter where he began to live as a hermit, all alone, for the next thirteen years.

(Source: The Promised Neverland Wiki)