Two identical lieutenants can be combined to create a much stronger lieutenant. Identical lieutenants have both the same name and the same amount of stars. For example, a two-star John can be combined with another two-star John to create a three-star John. However a two-star Mia cannot be combined with a one-star Mia because they don't share the same amount of stars. When two lieutenants are combined, the level of the new lieutenant remains the same as before. You can get more lieutenants to combine by completing challenge jobs, fighting bosses, or at the Favor Page.