He lost his father and grandparents in the 2011 tsunami and was left homeless.

From his Wikipedia page:

Sasaki is from Rikuzentakata in the Iwate Prefecture. Born in 2001, he was named after the villain Rouki from Hyakujuu Sentai Gaoranger, a Super Sentai show that was aired in the same year.

He was in the third grade during the 2011 Tōhoku earthquake. The resulting tsunami swept away his house. His father and grandparents died, while Sasaki, his mother, and his two brothers had to live in a nursing home during the recovery.

The family moved to Ōfunato the next year and Sasaki began to play baseball at his new school. He graduated from Ōfunato High School.