Sega is cross-marketing its Total War games, by letting you download a free pack in Total War: Shogun 2 by playing the iOS title, Total War Battles: Shogun. Upon completing the campaign in the mobile game, you'll get a key-code to download the Sendai Clan Pack for Shogun 2 via Steam.
Playing as the Sendai in Shogun 2 gives you a few stat adjustments; you'll get +10 to diplomatic relations and a 2-turn reduction time surrendering castles, plus -1 resistance to occupation and -3 unhappiness from differences of allegiance. Not a bad trade-off as a free giveaway for finishing the mobile title.
Finally, the iOS game will be adding a skirmish mode sometime soon. This will let you pick a difficulty level and go straight into battle, complete with the full roster from the campaign mode and new legendary units. So once you have finished the campaign and cashed in your free DLC, you can keep battling without all that story getting in the way of the bloodshed.