So you want to write a harem anime. Yay, you already have a themes for it, as well as the plot. As well as the harem members in question. But how about the protagonist? Simply put, the Harem Hero is the main lead in the entire story, oftentimes refer specifically to a male lead in a harem story with action elements (sometimes complete with Battle Harem and/or Magical Girlfriend).
BasicsCharacterization Tropes come as priority. You can have The Everyman, oftentimes acting as Audience Surrogate. Even then, you must avoid Flat Character at all cost. Simply put, add something that could flesh your character. Even if your character started out as uninteresting/unlikeable, Character Development is required. For example, a Dirty Coward could become a Cowardly Lion or someone who's supposed to be coward but charges ahead.
ReasonThere should be a reason why the girls are interested in our hero. The reason might be flimsy, but at the very least, it must be acceptable to the audience. A Nice Guy attracting a Harem due to kindness is overdone, but note that if applied correctly, Tropes Are Not Bad. Some show attempt to subvert this by having Hot-Blooded Jerk with a Heart of Gold as the base characteristic, where the kindness element is downplayed but certainly still exists. In stories specifically about Battle Harem, the Hero might be required by the Action Girls for certain roles (Mission Control, MacGuffin, Kid with the Leash etc). This gives him another role outside the obvious harem plot.
TypeThe hero of a Harem Anime typically comes in certain distinct flavors.