So, I was relaxing in my room and I just randomly thought of this, I haven't really thought it out.
Imagine there was a time skip, and somewhere in the time skip, Shikadai had a brother. His bother doesn't have the smarts, but he has discovered a new level of the Shadow Possession Jutsu: Shadow Control. It's basically taking control of the shadows around you, bypassing the downside of the Shadow Possession: You can't use it in the shadows. Brother quickly rises to Chunin, and eventually Jonin with his skill, and he has to fight an A rank ninja from another village. This ninja has taken down all of his comrades, and his brother, let's call him Shikamada, has to put all of his chakra into a special move. He kills the enemy but using that technique cost him his life. This, in turn, causes Shikadai to desert the village in anger. He becomes a missing-nin, and figures out how to use Shadow Control. He figures out that a person's shadow is attached to them, and he can take control of it. He uses this to steal chakra from people, planning to get revenge on the Leaf for allowing such a sacrifice. One day, he is out and about and runs into Team 7. The enemy that Team 7 is facing is stronger than them, and there s nobody around to help. Shikadai immediately takes control of the enemy's shadow and drains him of his chakra. He then uses the Shadow Sewing Technique to finish him off. Boruto catches a good glimpse of him and calls out to him. Shikadai runs away. Boruto chases him down and leaves his team. Boruto catches up with Shikadai, but Shikadai rebukes him and attacks him. Boruto and Shikadai have a short battle, with Shikadai coming out on top. Boruto, on the brink of having his chakra drained, uses Talk no Jutsu, and it works. Shikadai comes to his senses and they catch up to the rest of Team 7, and they all return to the village. Because of Shikamaru's effect on the village, and Shikadai's efforts to save Team 7, Shikadai gets a slap on the wrist and is eventually promoted to Jonin.
What kind of time skip are you looking for? The youngest Jonin we've seen was Kakashi at age 12-13, so even assuming that Shikamaru and Temari got pregnant literally immediately you're looking at a timeskip of at least 13 years to get Shikamada to Jonin, and that's only assuming that Shikamada would rival at least Kakashi.
Why would Shikadai even get angry with the Leaf? Shinobi die on missions.
Shikadai has no reason to rebuke or attack Boruto.
This isn't really a filler at this point. You're trying to change character traits and storylines and relationships. This honestly looks like fanon and there's an entire wiki for that if you wanna try to share your idea there. Here's a link