The way this uncle and nephew pair bond is through music. If anything, Viktor was the one who suggested picking up an instrument when he noticed that Axel was struggling with emotions and communication. Axel definitely took his advice, picking up piano on his own.
Whenever Viktor visits, he brings his violin with him, so he and Axel can play something together. Or at least just listen to each other. Viktor knows his own struggles isn't the same as Axel's but he knows how it feels to feel so small and helpless. He wants him to have something, anything to let out how he feels instead of going down a spiral.
Viktor cares for his nephew deeply, he wishes he can fix what has been tormenting Axel, but he can't.
