Master Fu worried about the boy that lay unconscious in the other room, a boy he had found surrounded by blood in an alleyway. Of course Fu had checked his injuries but he knew that the child couldn't be taken to the hospital for the same reason he'd been found at all. As the Guardian of the Miraculous he had the ability to sense what others couldn't and that is exactly why Fu was drawn there. Somehow the child had manipulated the field of Luck to bring help, it was something he had thought only a fully trained Ladybug to be capable of.
Fu had no idea of the willpower possessed by the fourteen year old. He had no way of knowing that the child's spirit was elsewhere until Wayzz had informed him of a shift in the seal. The seal that kept the kwami bound to the miraculous had weakened considerably. During this revelation however they had failed to react in time when the child, having been healed and with a promise kept, awoke and escaped.
Of course the two of them kept searching while keeping up Fu's double life and were forced to give up about two months later. The need for heroes was undeniable as the butterfly miraculous started being used with dark intent.
The next time they saw Luck, as Wayzz and Fu began calling the mysterious child, was during the new heroes first battle. He was perched on top of the roof watching the battle but what stopped them from taking action was the kwami that floated near his head. The kwami, like Luck himself, was something new as neither of them had even seen him before. When the battle finished they watched Lucky transform before turning and jumping away.
What had them worried was that neither of them had felt the new kwami's power meaning Luck wasn't sure if he'd use his powers for good or evil. Neither kwami nor Guardian were ready to turn an unknown into an enemy so they merely kept watch.
The next day was when Stoneheart reappeared and by a stroke of good luck Fu was close enough to the school to watch not two but four teens rush out. Chat Noir was suited up as he leaped off the roof and Marinette and Alya raced out the door. Fu prepared to follow when he noticed Luck leap out of a window on the first floor and ran towards an alleyway. Fu barely made it in time to see a flash of light as the boy also transformed to follow the others, probably.
