Have them be like an experimental group of hybrids. That should satisfy the avid reader!
Hmm but the hybrids are called cyborgs in my story (as in, people who lost a limb in an accident, or had their spines injured receive implants to be able to live a normal life). Normally such implants are only for health issues, not for improvement.
Think cyberpunk without the punk, the world is somewhat in a peaceful stage.
Then make them violent. For a younger group, let them be born with birth defects, ans they all knew each other because they were all roommates in the hospital, waiting to get their new bionic parts. Or for an older group, say like veterans who lost limbs in combat. Let's say the reason they all are like siblings is that they were a squad when fighting was going on. They all lost limbs/got injured in one tragic accident, and (this goes dor the younger and older here) they got "upgraded" as you will. They were then modified to become violent war machines, but something malfunctioned and they kept emotions and their humanity, but they were specifically altered to kill. And that's what would make them so likeable. Together as a team, they aren't villains, but when one is deemed to make a hard choice, between let's say, an innocent person, or a member of their team, the team member will always be chosen over the innocent being. Thus making the character lose their humanity over time. Until one as broken as they are comes in and makes it seem like the villain is oh so close to redemption, until the choice between a new friend and a team member is up for grabs. The team member will always be chosen, and the villain will stay the villain. Boom. Tragedy and heartbreak, and a likeable villain. Hope it helps!
