See “Ranmaru Mori Unlocked” for preparation tips. First you will need to reach floor 76 in survival mode, which is a task in itself.(it doesn't matter what missions you take to get here)On floor 76, choose the mission Woeful Beauty. On floor 76, you need to defeat Oichi. On floor 77, you have one minute to defeat Hideyoshi Toyotomi. On floor 78, you must defeat Ranmaru Mori and Mitsuhide Akechi in 3 minutes. You then must defeat Nobunaga Oda before he leaves the floor. On floor 79, you have to survive an onslaught of several generic officers at the same time. If you kill one, he will return in a few moments. Once you have killed the officers several times, Nagamasa Azai will show up. Defeat him and proceed to the next floor. On floor 80, you will fight Katsuie Shibata. Once you clear floor 80, Katsuie will be in the shop. To actually get the achievement, you have to hire him and save your game.