Your college buddy, Kaneki, was just released from the hospital. He was attacked by a vampire, yet despite everything he seemed alright...but you noticed something was 'off'. He didn't show it, but the attack did change him. He had become a vampire, but not by being bitten. Instead, his organs (mainly this heart, stomach, and liver) were replaced by the ones from his attacker. Even Kaneki doesn't know this, but he can definitely feel something has changed inside himself.