Lance is recovering from his time spent in the "ring" having sustained many permanent injuries he is unable to return to the ocean due to being unable to sense anything behind him. Lance is in the current custody of the Medical Merfolk Zoo.
During his time there at some point his tank needs fixed or cleaned and someone has to dive down into the deep where Lance lives. Lance is protective of his territory as anyone should be having not yet recovered from the abuse is still seen as dangerous.
Keith is sent down to repair something in Lance's tank and is unaware of Lance's presence behind him.
(I am new to archiveofourown so please tell me if I did something wrong or any tips about the website)