In addition to the Assassin's Creed crossover DLC, Final Fantasy XIII-2 will soon host some Mass Effect costumes. Starting March 27 in Japan, players will be able to outfit Serah and Noel in completely inappropriate N7 armor for 300 yen or 240 Microsoft Points. It is, at least, inappropriate in a different way from bikinis.
Though Square Enix would never release numbers (so we'll never know), we'd be surprised if this DLC took off in Japan. After all, Mass Effect 3 sold 8,142 copies there in its debut week.