Once Kieran's body overflowed with the energy provided by Vim Restoration, he ducked under Bundal's subsequent blows before moving in closer. He did this to reduce the chances of Bundal succeeding in the strange series of Imperfect Transmutations he revealed throughout their heated back-and-forth exchanges.
There were times when Bundal would change the state of his skin to make it rubbery and absorbent to damage. When that happened, Kieran switched from blunt strikes, like Wrath Eruption, Seethe Burst, Fury Rush, and powerful basic attacks, to precise slashes.
Moreover, because Bundal broke free of his restraints, Kieran had to hold off on unleashing Blood Pulse until the perfect opportunity arose—which was right now.
By the time Bundal revealed that something was amiss, with several alarms raising his mind to exercise caution, it was already too late.