Ryu ga Gotoku Ishin (released in Japan in February 2014) is a spin-off game set at the end of the Edo period of Japanese history (known as the Bakumatsu period), a period when the Tokugawa Shogunate came to an end and imperial rule was restored (Meiji Restoration).
Sakamoto Ryoma is living undercover, with a false identity, as "Saito Hajime" in Kyoto. One year earlier, on the eve of the coup d'état of Tosa, Ryoma's foster father, the man who raised him, was murdered before his eyes. The only lead he had to discover who the killer was is that he used the Tennen Rishin style of fighting. This is a style used by the Shinsengumi, so Ryoma infiltrates their ranks, becoming captain of the 3rd Shinsengumi unit, in attempt to find the killer.
Big thanks to Kevin Debrabandere for creating a PDF for the entire Ishin guide. You can download the PDF version of the guide here. Please be advised that the PDF is outdated now, but still contains information for the whole game.
You can do this at the start of Chapter 10 and after you have completed Substory 32: More Tattoos
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Go here and Ryoma sees Sumibozu again. He's got a lot more tattoos than he had before and also has shaved his head, saying he's been doing a lot of mental training. He says he's ready to challenge Ryoma one last time. Talk to him and choose the TOP OPTION to accept his challenge.
After Ryoma beats him, he says he'll stop his services and that while mental training, he found something worth doing. He thanks Ryoma for helping him to find enlightenment and gives him a Haisui Talisman. You are also rewarded with 400 Dharma.
After completing the substory, go to the bottom of the steps near the entrance to the Shinsengumi HQ in Mibu and talk to him to get a Super Rare Attack Soldier Card. Note that he does not appear until after the story event in the Shinsengumi HQ (after Hijikata tells Ryoma to go to the docks in Fushimi).
After completing all 67 substories and every Battle Dungeon mission, go to the Battle Dungeon reception to trigger an event (triggered automatically after completing the final battle dungeon mission, if you have already completed the substories). The receptionist tells Ryoma of a man with great skill and wants Ryoma to help deal with him.
When you are ready, select the final battle dungeon mission (20: Defeat Toyotomi Hidebu). When you enter the room where you faught Toyotomi, an event is triggered and you fight Amon Genjuusai.
After defeating him, leave the Shinsengumi HQ area, then return and go to the reception and Ryoma will be told about a challenge to a fight from Amon.
Go to Kiyomizudera and fight Amon Genjuusai again.
This fight is no joke. This is the hardest fight in the game, so come prepared (plenty of healing items, etc). It is actually possible to disarm him (using the sword style, R1+Circle counter), so you can make your life a lot easier by taking away his sword.
After defeating him you get the Enchanted Sword that Time Forgot weapon.
