Nightlingbolt
AKA Nightlingbolt
I'd like Hau to appear at some point, but if he does, he'll probably have had a massive falling-out with Hala prior to Ash arriving in Alola, explaining Hala not mentioning him up to now. That said, there is precedent for rivals not appearing in the anime (namely Silver and Hugh). Remember, Kukui and Burnett weren't even dating at the start of SM, and who knows? Maybe Hau is in Team Skull as a balancing force for Guzma's temper (in the games, he always seems calmer when he's talking to Hau).