When your identity and profession are centered around being a quintessentially tough and ruthless protector of everyone around you, how do you lighten up and make friends?
Friends is the story of Killer T, a squad leader of Killer T-Cells who protect a human body. Even though he's a respected and admired leader who can slaughter pathogens with the best of them, he's grown tired of the hyper-aggressive, aloof, and grumpy personality that's left him without close friends and unable to enjoy some of his interests openly. And so, the story is about his efforts to reach out and make friends without compromising his tough-guy image...usually with hilarious results.

(Source: TV Tropes)