Summon Night: Twin Age

From a very young age, the human girl Reiha displayed great aptitude for
the magical art of Summoning. While still a child, her powers caused a
terrible accident during a major Summoning experiment. It was reported
that Reiha had died as result, but she survived, along with a young
Summon Beast named Aldo that had been pulled into her world...

Following the accident, the two children grew up together as brother and
sister on the tropical island of Jarazi, among a race of people with
beast‐like features. There they learned to commune with the Nature
Spirits that surrounded them. One day, the Spirits began acting
strangely, prompting Reiha and Aldo to investigate. Their quest to find
out who or what is behind the corruption of the Spirits will lead them
back to the human lands where the ataclysm first brought them together…