According to Fandom(novel-based spoilers)
Lu shi shared his power with lu Xiaoyu, they both are reincarnations and she knows about her previous life as well.
My personal views
I completed that anime long ago, and lu shu got awakened when he saw that superhuman with firepower doing a magic show on the street(his locket reacted the first time and he was able to see an awakened person in slow motion) along with his sister but he didn't know it at that time. Later he met with an accident and his power got self-activated and his locket is somewhat related to his awakening. As you can see magic items can make an awakened person more powerful, like ruins items or spirit stones. Even the magic apple he creates has magic abilities like healing her sister's illness. Seems like this item come from another dimension having magic items but I am not sure about that point.
So now finally I come to your answer, that black magic paper went inside Lu Xiaoyu because that nebula map is totally opposite of lu shi nebula map, also lu shi is already awakened person and that nebula map(black paper) has the power of awakening just like lu shi locket.