Kasius is the overseer of the Lighthouse.
In "Orientation: Part 2", after Simmons saves the life of one of Kasius's human servants, Kasius has Simmons brought to his suite and asks why she violated his "a life spent, a life earned" policy. Simmons responds that she only did what she thought would make him happy which he refers to as the "superior answer".
Kasius then orders his Kree soldier, Sinara, to issue a "renewal", the Kree version of population control, in order to relieve the guards burden.
Later, the servant who Simmons saved returns, but when Kasius notices a fresh scar of the man's face he comments how his servants must represent perfection. Sinara then kills the servant and Kasius removes a liquid metallic device from the man's ear. Kasius then places the device in Simmons' ear which makes her deaf and at the end of the episode Simmons is seen being dressed in a servants uniform.
In "A Life Spent", Kasius orders Simmons to "fix" an inhuman girl named Abby. Abby explains to Simmons how whenever a human turns eighteen Kasius exposes them to the terrigen mist to check if they're inhuman and if they are then they have to demonstrate their powers at a ceremony. However, if they can't demonstrate their powers then their families are punished.
Later, it's revealed that this "ceremony" is actually an arena fight where Inhumans are the gladiators. Abby uses her powers to kill her opponent during the fight which impresses Kasius's guest, a red-eyed alien named Lady Basha.
After the fight, Simmons watches as Kasius sells Abby to Basha and Kasius thanks Simmons for all her hard work as he was able to get a high price for Abby.
At the end of episode, Deke informs Kasius of Daisy's attempt to rescue Simmons allowing Kasius to set a trap for Daisy and capture her.
In "A Life Earned", Kasius interrogates Daisy and makes her tell him the story of how she and Simmons came to the future. Furthermore, Kasius warns her Mind Reader will be listening to her thoughts and he will tell him if she's lying. Daisy tells her story to Kasius, but says only her and Simmons came through the Monolith portal. Kasius next interrogates Simmons and warns Daisy that if Simmons' story is different then they both will be punished. However, Kasius is happy to hear the same story from Simmons thereby extinguishing his fears.
However, later, Mind Reader warns Daisy he also read Kasius's mind and tells her that after Kasius sells her he's going to leave Earth forever and destroy the Lighthouse and humanity along with it.