Tier 1: The Most Important (and who they ping for)
Apple - huge ping for Son Goku. They first met when Eyepatch brought him over to Moon's house and again when the Twister party happened. Apple wormed his way into Moon's cold, dead heart by eating a lot, being clingy, and liking Moon for some unknown reason. They live together in Section 3.
Eyepatch - huge ping for Sha Gojyo. They met over the journals first and later in person when Eyepatch dragged Moon out to the bar. He drinks, he smokes, he's a redhead; the similarities are uncanny. Moon is likely to call on Eyepatch when he needs to drink until they can't feel feelings anymore.
Bastet - huge ping for Cho Hakkai. She was the first person Moon met after his Greeter Charger, and he likes the way she doesn't put up with anyone's bullshit (even his). She can use her energy to heal him, she pokes at the cracks in his armor, and she can make him do stuff just by smiling at him.
Tier 2: People Who Don't Annoy Him... Much (and who they ping for)
Koi - pings for Koumyou Sanzo. Met when Koi saved Moon from being trapped under a burning building during the fire. He feels fatherly and Moon still feels as though he's in debt to Koi.
Meatbun - duh. This is Son Goku. That's also who he pings for. Moon adopted him into the home because he had a memory of rescuing Goku from the cave. They met in the Bazaar by chance one day and recognized each other.
Cara - pings for Yaone. He mostly talks to her over the journals, but she takes care of Meatbun and Apple when he can't, and she did help him get unstuck from his fridge. She seems caring and compassionate.
Stoneface - slight pings for Kougaiji. Someone who acts more callous than he actually is, and someone who commands respect from his soldiers, people who are ready to die for him. Moon met Stoney when they were elevator'd together in a Memory Lane Event.
Youth - slight pings for... maybe Zakuro for Exclamation Points! Moon first met Youth when Youth revealed he had received one of Moon's memories. He met Youth again in Disney World and during the Apprentice event. He thinks Youth is slightly off in the head, but means well.
Bell - pings for Gojyo for perverseness. He met Moon for the first time in Disney World and again when Moon was apprenticed to him. Moon has a neutral opinion of Bell.
Tier 3: People He Doesn't Like (and who they ping for)
Smoke - pinged for Gojyo because hmm, that's who he is. They first met when Smoke punched Moon in the face for existing. Despite Smoke's attempts to rekindle their "I'm From the Same World" bond, Moon wasn't willing to give him a second chance.
Ghost - not sure who he pings for, maybe Dokugakuji for the attitude and backing Smoke up? He met Ghost at the bar the same night that Moon got punched. Ghost stood by and did nothing but laugh. Moon is still not amused.
Juliet - pings for Kami-sama for being amused by murder. Met during the Memory Lane event when they witnessed Stoneface's memory.
Grift - pings for Gojyo for the teasing. He's mostly spoken to Grift over the journal, and the other man seems to love pushing Moon's buttons.
Lin - pings for... himself? in the antisocial department and attitude. He's never met her in person, but he doesn't like how she stalks Bastet all the time.