Adding a theme to an Event or a Reign is a great way to get everyone involved in some form of role-playing. Wandering Ronin encourages themed reigns and events, and the players should make the most of these themes, to include possibly getting themed garb to making themed weapons and characters. A theme unifies the chapter who uses one, be it through people attempting to role-play up to the theme or people rebelling against the theme and making themselves the enemies of that reign.
A themed ent is a pre-planned event (Coronation, Mid-reign, etc) that is set up with a theme and a goal in mind. You may simply have it be a theme of Company Wars to a Quest to slay a group of monsters. Remember to make sure your entire event follows the theme: from the promotion of it to the food served to the games played. The closer you stay to the dedicated theme, the more your players will want to participate in it.
A themed reign is a longer period of role-playing. The monarch may decide that the theme for his reign is that he is a brutal tyrant who will oppress anyone that wears green. He may also decide that anyone who wears pink flowers on their garb is eligible for some role-play only award called the Order of the Fairy Lily (nothing that is listed in the Rulebook may be given for this type of behavior in response to a theme). Use your imagination when thinking of your theme for the next six months, and consider it carefully: you are responsible for carrying it out. A good way to stay on theme during the reign is to designate the second battlegame of the day always concerns the theme.