Lu Bu is often portrayed as one of the most formidable warriors in Chinese history, and is no exception. You'll encounter Lu Bu several times throughout the main campaign of, beginning in Chapter Two, but it's not until a pivotal battle much later on that you actually have an opportunity to defeat him.
Usually, his sudden appearance means you have little recourse but to flee; he functions a lot like Mr. X in during certain missions, forcing you to abandon strategic points and run for your life.
Finally, during the mission "," you'll be able to face Lu Bu in one-on-one combat, and, with a lot of skill and a little luck, defeat him for good.
Just don't expect him to be easy, just as he is in every game where he appears. Lu Bu fully lives up to his reputation, delivering devastating blows both by himself and astride his steed, the renowned Red Hare, and you'll need every tool in your arsenal to defeat him.
By the time you've reached Lu Bu, your build is probably pretty well set in stone. Still, you'll want to double-check everything in the Battle Preparation menu.