Ruby noticed Onyx had been looking pretty tense as of recently, maybe he was having a bad day, maybe that flirty Leavanny from their last job got to him somehow. Either way she felt like she should at least try to help him out with his stress, it's what a good friend and right hand of the team would do. There's a beach nearby she could take him to, maybe the nice ocean smell, bright day, and warm sand would help ease him from this tension, so that's exactly where she took him.

Upon arrival however there was one small detail she forgot about... this was a nude beach. This did not help much with what Onyx was going through, being surrounded by so many exposed pokemon like this was definitely getting on him, and it was very noticeable. Onyx's urges rose and he felt he needed to do SOMETHING to satiate it, and fast, when a large Goodra came walking past them, that was the point that did it for him.

...They both feel like they're gonna be here for a while.