The friend heart is actually a pretty terrifying concept from an outside view. You go about your day with some of your closest allies. Then you spot this kid who the king told you to defeat. You know the king is possessed right now and the kid often saves the king, but orders are orders, regardless of possession.
So you attack. But before you realize, the kid summons a pink heart, glowing soft, warm, and deceptively comforting... almost beckoning to be touched. It doesn't touch Kirby however, merely floating a few inches above his hand. It refuses to make physical contact with his body. You snap out of your trance too late. He's already thrown it.
The heart makes physical contact, but rather than any pain, like any of Kirby's normal attacks, it phases through you, absorbing and dissolving into your body like cotton candy in water. It vanishes in less than a second, leaving only a few fading sparkles and a slightly pink hue from where it entered. Yet you don't feel any different. You look at your friends- they're just as confused as you are. But then; it hits.
Not pain, nothing like it. A strong euphoria, completely wholesome, nothing like what would come from adult enjoyment (Yes i needed to say that bit for proper clarification so you don't get the wrong idea). Your heart beats faster and faster, abnormally so, yet it doesn't hurt. In fact, nothing hurts. Even the aching shoulder you were ignoring for over a week was painless. But through the euphoria, it felt like something was changing. The kid, Kirby. You felt an increasingly powerful affection toward them. You wanted, no.. you *needed* to be friends with that entity. And as the feeling swept over you, you turned back to look at your friends, their concerned expressions. Something about them felt wrong.. like they would take Kirby away, like they would take away this euphoria. What.. what if ... No. You wouldn't let yourself even think about that. Behind the bliss, new emotions began to swirl. Distrust, rage, jealousy. You wouldn't let them take this away. Not when you could be spending your days playing with Kirby, taking naps in the summer sun, baking pies of all flavors, coloring on paper, swimming in orange ocean.
They were the problem. They needed to go. So you attacked. Kirby didn't even tell you to. You don't even remember if he wanted you to or not. But what did you care? They were going to interfere, they could possibly even hurt Kirby. You couldn't feel the pain anymore anyway. Heck, you could probably die and still not feel a single bit of pain. It felt as though Kirby would revive you anyway if you did. You didn't even know how he would manage to do that. You didn't care for any of that, nor for the terrified faces of those who were once your closest friends as you attacked with no hesitation or restraint.