Before Leo joined the army he was used as a test subject for Haidra that would be used to replace a heart. Subjects who survived the procedure usually died from being treated so horribly during and after, but Leo's the only one to have survived it all.
Oh, and I recognize that Leo's Haidra is on the right side of his chest instead of the left. They didn't remove his actual heart, they just inserted the Haidra and used magic to stop his heart manually.
#gLeo #YuliA #twCharas