He might be just a cat, but Mango holds a special place in Mia's heart. Check out what she says about her furry friend:
Mango slides across the freshly waxed front hallway and leaves a mango-colored streak behind him. A wonderful magical mango streak that fills my heart to bursting. (10.173)
Aw. True love, right? But Mango isn't just any ordinary adorable cat—nope, Mia believes he has the soul of her grandpa. She found him on the day of her grandpa's funeral, see, and ever since, the cat has helped her feel close to her beloved grandpa, long after he's gone.
This is why it's such a big deal when Mango dies. Sure, Mia's sad to lose her pet, but she's also bummed that her grandpa is no longer near her. Poor Mia.