For the reason that Calliope can aid the Champions in the near future, Hal decided to give it a chance to prove itself worthy of his mercy.
After the debacle yesterday, Eli gained the ability to interpret the summoned creature's language. That motivated her to try harder in convincing Hal to spare it. She listed down all of its potentials, promised to take responsibility, and guaranteed its loyalty to her, which eventually gained his consent, but with the conditions that Calliope would only remain as guard inside the library and stay out of people's sight.
"A bird and a bookworm. How befitting."
Eli was happily brushing Calliope's smooth feathers when Hal came into picture, watching them with a teasing look. His mockery only fell on deaf ears, though. She just beamed at him before replying cheerfully, "That's right! Calliope and I are meant to be, after all."
For unknown reasons, that seemed to irk him.
