Details: After catching Guzzlord and returning to Anabel and Looker in the Seafolk Restaurant, they will suggest reporting to Wicke with all the Ultra Beasts now being captured. Once you arrive in the Labs Area of Aether Paradise, only Wicke and Anabel will be in the room. However, shortly after arriving and talking to them, Looker will burst in the room in another frantic state.
Looker will claim that Guzzlord wasn't the last Ultra Beast, that he has just seen one fly across the sky of Alola. He describes it as a massive black figure that still has the power to reflect light and brightness, one that looks similar to the rest of Ultra Beasts. But Anabel will quickly respond that there is no more word on any Ultra Beast sightings; Wicke confirms this, telling she would be the first to know of such with the technology she has at her disposal. (The Pokemon ends up being the Legendary, not Ultra Beast, Necrozma.)
Ultimately, the two suggest that Looker must be mistaken, that he must be seeing things after being as tired as he is. And, reluctantly, Looker finally agrees to this notion, being told that him and Anabel have been given paid vacation from the agency for their efforts afterwards. Anabel will then leave to meet up with Nanu, while Lookers says he's going back to the hotel on Melemele Island for so much needed rest and relaxation.
The Ultra Beast Storyline officially ends with Looker giving you a token of his gratitude for all your hard work in the form of one million Poke Dollars.