Calm, serene. Yazoo rarely has fits of rage or anything like that. He is one of Sephiroth's Remnants, along with his brothers, Kadaj and Loz. Whether he likes it or not, he also wants to find 'Mother'. That is, Jenova. It so happens that, to achieve this, he will have to manipulate someone. One of the former members of Avalanche — which, in this case, is you. Yazoo has been manipulative enough to make you believe that he is your savior, not all those you were with before.