When you happen to run into Clarke, you gain a troubled artist in need of the inspiration you can provide. Once he has found a muse once more, he can build a theatre for the residents of your Eiyuden Chronicle: Hundred Heroes castle town and your team to enjoy.
Clarke is found standing next to the fountain in Ardinale during Nowa's mission to help Norristar. You'll need to check the general store in Ardinale for the Star-Cross'd Lovers script and have the 5,000 baqua to purchase it. It is randomly generated so if it isn't there, you will have to play for another 30 minutes in real time and check again. It's a bothersome process but once you get it, you get to recruit Clarke.
Once you've built Clarke's theatre, you can choose allies to put into a play and see the show. Different combinations have different outcomes, some offer rewards! The theatre is on the west side of the HQ.