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Unlike the creation of Mewtwo in Gen 1 where it was designed to be the strongest pokemon ever but also suffered from having such a savage heart, Null/Silvally was created for a very specific purpose. Although, it was supposed to possess a similar ability to Arceus in order to help subdue and or kill the Ultra Beasts, it was noted that Null went on a rampage during tests in the Aether Foundation labs. Many of the scientists including Faba have found a way to keep its latent powers in check with the restraining mask that Null wears, however, during the creation of Null, Wicke was the only person in the participation of creating Null who was capable of giving it a good heart. She also managed to encode ways of feeling emotion into the Memory Drives so that the RKS System and the Null models would sync accordingly. (in case they were needed to change its type) This new sense of emotion along with the Memory Drives further reduced the risk of rampage and ultimately, it would give Null a new sense of life. The mask not only helped restrain its rampage, but it also helped it become more self-aware of its surroundings as it developed, and thanks to Wicke, self-aware of the life around it.
After Gladion stole Null from the Aether Foundation, it was as if a part of Wicke was watching over him, especially when Gladion had no one else to turn to or support him. It was as if that piece of Wicke took care of him for over the next two years the same way that she took good care of both him and Lillie back at Aether Paradise before they both ran away. After all, it's safe to say that Wicke was more of a mother to Lillie and Gladion than Lusamine was to her own children.
It's pretty interesting and crazy how a synthetic pokemon made in a lab can evolve from Happiness as opposed to just man-made objects.
inb4 I get flak for the whole emotion untangibility thing. Crazy stuff can happen in the world of Pokemon.