A character who you can feel a real connection to, somebody who will play big role not in the story but for your character on a personal level. The two of you take care of one another, you do a task for them and they do a task for you, heart to hearts, cover one another when mistakes are made. Sometimes there’s a special bond unique only to the two of you. It really makes the character feel human. I’m not talking about romances either, I’m talking companionship and friendship.
And if they’re not a friendly NPC, a satisfying rivalry between the two of you. Respect and honour is expressed to you both and when the time is needed, you team up and become the epic badges duo for a short time.
Examples:
Jenny Yu (Heroes Rise)
Emma (Zombie Exodus.)
Commander Hawkins (Mecha Ace.)
Ashleigh Wakefield (Deathless.)