Wei Song and the Central Plain's wishful thinking was to let Norland fall apart as soon as possible. Whomever benefited from its division was not particularly important.
For a long time, the main threat to the Central Plain had been Norland. No other power, whether it be the Dragon King or the many small kings inside Norland, was more powerful than the entirety of Norland. So, no one alone was a deadly threat.
Wei Song had long been wishing to prove his power. Naturally, he thought of resorting to assassinations. The Central Plain had quite a few skillful kung fu masters, but he had learned over the years that martial arts were not the only requirement to be a killer, nor was it even very important for the job.
He needed a professional killer.
Golden Roc Fort was an impossible choice. The only remaining candidate he could think of was Gu Shenwei, the "son of a friend", who met all the requirements of an outstanding killer.