Miracle's first meeting with Granddaddy Opal doesn't exactly promise a loving relationship. He catches her falling down the stairs of the basement when she's going to look for Dane's stuff and tells her to "be quiet about it" (3.56). Nice to see you, too, Gramps.
To add insult to literal injury, he also tells Miracle that "if your mama was dead when you were born, then you were never born" (3.81). Yikes. If you want to strangle Granddaddy Opal with the sash of Dane's bathrobe over that remark, you're not alone—at first glance, he definitely seems like the worst possible definition of a crotchety old man.
But once he gets to know Miracle, something interesting happens: He changes, and as Miracle's view of him evolves, ours does, too. It's tough to pinpoint the exact moment when this happens, but we're pretty sure it has something to do with him seeing Miracle's peers "hanging out the windows" of the bus teasing her about the bathrobe (4.20). Our best possible explanation is that witnessing the abuse she takes causes Granddaddy Opal to see Miracle as more than just a scruffy kid and recognize that his comments from when they first met hurt her feelings.
Whatever the precise reason, Granddaddy Opal clearly tries to make their rocky start up to Miracle. And he pretty much nails his attempts, too. He is everything that Gigi fails to be—he allows Miracle to secretly pursue her dream of becoming a dancer, gets her a bicycle, and lets her help him in the garage with his fledgling seatbelt-painting business. Probably the most crucial thing, though, is that Granddaddy Opal grows to care deeply for his granddaughter's wellbeing. Check out the part where he discovers her bruises from dance while teaching her to ride:
He blinked at me and I saw his eyes looking so wet, so full of water […] I had this vision of all that water pouring from his eyes, gushing out like two giant waterfalls. (6.64)
Of course, Granddaddy Opal's loyalty to Miracle also comes from another pretty disturbing place: He knows exactly what Gigi is capable of. Having been closer to his son than Gigi was, Granddaddy Opal knows that his son's heart wasn't really in Gigi's dream of him becoming a writer. As he rails to Miracle:
"What does she think you live on, air? How does she think it's all happening? Magic? She ain't doing it, that's for sure. And I shouldn't be doing it neither because the day will come when she'll take a notion you're going to be the next great something or other and away you'll go from here!" (6.20)
How does he know this? Because he watched the whole situation with Dane go down. He knows that Dane had no interest in being a writer, and that his real interests were in doing artistic activities with his dad. He also knows that if Gigi hadn't tried to interfere with his situation with Sissy, Sissy likely wouldn't have killed herself. In Granddaddy Opal's eyes, Miracle is his chance to take control of the situation in the way he didn't with Dane. Lucky girl.