If Akatsuki wanted to obtain Natsuya Yoruhana, he knew that Seiji Haruta would obstruct him.
He considered it quite easy to get rid of this trash from the Haruta Family. However, he didn't know how Yui Haruta would react.
Akatsuki didn't want to make the "Qilin Girl" his enemy. Although he was confident in his own power, she was at another much higher level than him, and he knew that it would be nothing more than suicide to go against her. The last idiot that challenged this Qilin Girl directly was burned to death and left as nothing but ashes together with all of his Spirit-branded Retainers! There was even no need for a cremation!
Since he was uncertain what exactly Yui Haruta's attitude was towards her exiled younger brother, the best move for him would be to prepare for the worst-case scenario that she still paid attention to what happened to Seiji Haruta. He felt that was the wisest and most cautious move to make.
