Donkey Punch

While on a holiday in Mallorca, Lisa (Sian Breckin), Kim (Jaime Winstone) and Tammi (Nichola Burley) meet four young men, Bluey (Tom Burke), Josh (Julian Morris), Sean (Robert Boulter) and Marcus (Jay Taylor). After spending the day at the resort together, the girls are invited to the men's yacht where they plan to party out at sea. While aboard the boat, they take drugs and the conversation turns to sex, and in particular, types of sexual acts. Bluey describes a sex act called a "donkey punch" which involves punching the female in the back of the head while having doggy style sex in order to increase the sexual pleasure for the man.
Marcus, Bluey, Kim and Lisa go to the master bedrooms where they begin having drug-fuelled sex, watched by Josh who, in the knowledge of all involved, lingers furtively in the darkness, recording the action with a camera. Bluey, who is copulating with Lisa, asks Josh to film the action and then decides to let Josh take a turn. Josh and Lisa then have anal sex. Immediately prior to ejaculation and with Bluey's encouragement, Josh donkey punches Lisa but uses excessive force, breaking her neck and killing her instantly. To cover up the incident, the men decide to throw the body overboard while the women want to report it to the authorities, and argument ensues about what to do with the tape. Bluey continually insults Tammi and in a fit of rage, she stabs him in the chest with a penknife, and the women escape in the yacht's tender. However, the girls soon realise that the tender's outboard motor is missing (a cut scene shows it still attached to the yacht). In a fit of despair, Tammi fires a flare, attracting the attention of the men. They quickly locate and pick up the women.
As the men attempt to get the women aboard, threatening them with a shotgun, Kim shoots a second flare directly at Marcus. The flare explodes into Marcus's torso and slowly burns him to death. Josh locks the recaptured women in one of the rooms below. Sean asks Josh to "call in" and request medical assistance for Bluey. However, knowing that Bluey still has the tape that contains footage of him dealing the earlier fatal blow, Josh instead decides to discover its whereabouts by torturing Bluey. He does this by withholding pain numbing drugs from him. Bluey reveals the location of the tape, beneath the bed in the state room. Tammi escapes the room by smashing through the glass door and cutting herself, and overhears Bluey mention where the tape is. She frantically roams the boat trying to locate it. She does this just moments before Josh attempts to retrieve it. Unable to find the tape, Josh returns to Bluey, stepping up the torture by turning his attention to the knife which still protrudes from the wound. Josh ultimately takes this too far and, following Bluey's pained protestations that he has already revealed the location, he twists the knife further into the wound before pulling it out, causing Bluey to die.
Sean tries to bring the situation under control by retrieving a shotgun from Josh. He then tries to calm both Josh and Tammi from a frantic argument about the whereabouts of the tape. Kim notices Sean holding a shotgun with Josh and Tammi visibly upset from an adjacent room. She misinterprets his intentions towards Tammi and Josh and brutally kills Sean with the propeller of an outboard motor. After realizing her mistake, she manically commits suicide by jumping overboard, leaving Josh and Tammi as the only ones left. A distraught Tammi decides that she cannot remain on the boat any longer. Josh agrees, and readies the tender. His plan is to leave the yacht, get back to shore and claim that there was an accident. As Josh pushes the tender away from the yacht, Tammi quietly takes hold of the end of the mooring rope at the stern.
Once the tender has floated some distance from the yacht, Josh pulls his hunting knife from his shorts and points it at Tammi. He demands the incriminating tape from Tammi and, fearing for her life, she obliges, throwing it on the floor of the tender. As a distracted Josh reaches for the tape, Tammi quickly throws the looped end of the mooring rope around his neck. The rope immediately reaches the end of its tether and Josh is wrenched into the sea, snapping his neck and killing him. Tammi, now the sole survivor, fires a distress flare in the hope of being rescued. She then lies down on the tender and morbidly stares up at the night sky, as the raft drifts away into the ocean.

Question: Who kills Sean ?
Answer: Kim kills sean.