IntroductionDonald wants you to cause a gang war in order to make property prices decrease for his benefit.
Breaking KenjaminYou need a Cartel Cruiser, if you didn't keep one from that last mission, get one from Aspatria. Next you need to go to the Multi Storey Car Park in Newport. Head all the way to the top and do not get out of your car. When you reach the top floor, quickly run over or drive by Kenji and then go off the ramp to escape. You must leave some witnesses though so try to just kill Kenji. After you've made the jump you need to escape Newport, so head towards Belleville Park and exit the vehicle to pass the mission.
Additional NotesNow that you've killed Kenji you can no longer accept his missions. I hope to god you had already finished them before doing this or you'll never get 100% (providing you saved the game).