Anyone looking at Bastion for the first time might rightfully believe he was a cruel, unstoppable killing machine, and in many ways, they wouldn't be entirely wrong.
He was certainly programmed to be exactly that: A robot constructed for no other reason than to murder and destroy all that stood in his way, but he had rebelled against such a terrible fate.
Bastion refused to be what his creators expected him to, determined to find another way of living. Determined to heal and love instead of kill and destroy.
And in his search for life, for happiness, he discovered his love for nature. Animals, plants, whatever breathed or grew organically, he was intent on saving.
Nature was also safer for him to remain in, away from humans when he lost his temper when the Omnic Crisis hit him unexpectedly.
He hoped one day he wouldn't need to hide, but in the meantime, he was happier there, in the wilderness, away from everyone he could harm while lost in his intended program.
"Ganymede, sing for me," Bastion thought.
He couldn't speak, he wasn't programmed to, but still, his bird knew him well enough that the sounds he emitted were understood nonetheless, and he began to sing a merry tune.
"That's it, sing, little bird, sing!"