Year 1813: He was born as the Koutaishi (Crowned Prince). He was given the position over his twin brother because he was fully Ryuko and Tsuhi was half Aetherian.
As an egg he and his brother lost their mother when Ryuuguu was attacked by The Demon Gate. They hatched four months later with their fathers adoring them both. However they still wonder about their mother and who she was. They didn't lack for a woman's touch. Funny enough Tatsu did a great nanny job and Julie was also there to lend a hand. They were adored by their parents and their care takers.
Year 1818: When he was five his brother was assaulted with Cursed Arrow. Who shot it was never found. The arrow missed his father who was the target and hit Tsuhi. His brother nearly died from the wound it made as it went through his torso. They were able to take the arrow out and heal Tsuhi with chi techniques but they could not remove the curse on him. He began to wither and die. Saizo's 'Uncle' Kaidan and his father Kogashimasu left on a trip to one of the ancient monasteries to beg the dragons to save him. Apparently their prayers were answered and Tsuhi's health came back to him just before he died.
Year 1820: When he was seven him and his brother were kidnapped as they traveled between the Snake Clan and Ryuuguu. The cult that took them worked under Mouko and was going to sacrifice them to their akuma lord. The boys were saved by a tengu named Doji. He escorted them home and taught them techniques of the Tengu Clan.
Year 1823: When he was ten his brother, ever skilled at getting into needlessly large amounts of trouble, was kidnapped by Mouko. This brought a lot of things into 'focus' for little Saizo. The first was that his brother was weak. The second was that his 'mother' Kogashimassu loved Tsuhi more then him since the two had a 'connection' of a spiritual nature and Saizo had no such thing. This brought up a strong jealous nature but he still sucked it up to rescue his brother from Mouko with the help/guidance of Doji.
Once the whole affair was behind them, River took more seriously the grooming of his crown prince for the future Genpukku and dragon slaying. He also apprenticed him under Arashi.
Year 1827: As a preteen Saizo did many rash things that would be considered less then intelligent. The first was to appraoch Nariko for a secret affair at the age of 12! He was thrilled that she agreed, though she asked to wait until after his genpukku which he agreed to. This was the highlight for him, in comparison to having his brother become a big jealousy issue in his mind. He hates his this consumes him and yet he cannot help but feel the rage rising inside of him.
Year 1828: His homeland falls, his father and brother are taken prisoner, all the span of a few days. Saizo rage hits a maximum, feuled by his depression. He becomes obssessed with taking up as Emperor for his missing father.
Year 1829: He meets Clover shortly before he takes off for his Rite of Ascension via dragon hunt.
Year 1830: He rescues Arashi from the humans and helps him save his dragon bond.
Year 1831: Saizo kills a dragon and claims its heart. He renames himself Muramasa.
Year 1832: He returns home and is crowned Emperor. Shortly after his return he asks to dump Sachiko and pass her onto his brother as he has not interest in her and Tsuhi cares about her a lot.
Year 1834: Clover warns him that Kohana is looking to get back with him. Outraged by the notion, Kohana loses all chances. However at this point Clover comes onto his radar and Muramasa opts to date her.
Year 1835: After a year of playing around dating Clover despite the dangers (after assassination attempts he does assign Shinobi to watch her of course) he gets a reality check about how he cannot marry a non-ryuko woman given his position. He dumps Clover harshly (hoping it will allow her to move on, it doesn't) and then arranges himself a nice upstanding courtier wife he will never love (Naomi).
Year 1836: His mother's spirit talks to him through Shoukin and he learns, unhappily, that she is disapointed in who he has become. She wishes he was "Saizo" again. She also hints his father might be alive but is too vague about it for him to put his hopes on it.
He marries Naomi.
Year 1842: River reappears as a child, having escaped the Land of Dragons via the river of souls. Not wanting to take the throne from his son, they arrange for his "true" identity to be covered up. Naomi and Muramasa pretend he's their son and a namesake of Muramasa's father (instead of actually BEING him).
Year 1843: River was in the aetherian school, Legacy Institute, when the capitol city fell. He protected his fellow students using his paladin powers but as a result many in his homeland suspected his true identity. Those with political weight even started to push for him to take the throne.
He eventually hears that Clover has been in trouble for almost a year and his concern for her outweighs his desire to cut her off. When he comes to her aid though he finds her kissing Chestin! Furious he returns home without letting her explain.
When Clover tracks him home and attempts, once and for all, to offer herself to him. He is touched, but he rejects her, claiming she is in love with loving him instead of with him. If she truly loved him she wouldn't want him to suffer. However, she sees him as cold hearted and is furious. As a result she opts to give up on him and instead focuses on making something of herself and travels with Chestin's trour group.
Year 1855: With the threat of the Slada’sha rising, the powers that rule the nations/factions come together (Chestin, JJ, Scathe, Chester, Xiphil, Muramasa, Kaidan, Oseron, Kallista, Leorajh) to discuss how they should handle it. They agree to assemble teams to investigate various issues. One team will look into the catacombs under Cardinal Meridian for more clues, since a Slada’sha had slumbered there. Another will investigate the strange calling from the ocean and where exactly it is. A third will look into Sardor Isle and see just how asleep the Slada’sha there is now. The last will look into the ruins of Aether’s ancient capitol in what is now Nazca and see if there are any artifacts that may have been stored for use against these creatures.
During the forging of the Dawnbringer's Pact, Oseron takes the information and holds a meeting with JJ, Chestin, Scathe, Chester, Xiphil, Muramasa, Kaidan & Leorajh. They realize that the other Slada’sha are stirring because of the big one waking up, someone the emanations are waking others. Mouko invites himself into the meeting, declaring that previously waking them required his power so he isn’t sure how this is happening. Realizing this is a world threatening issue, they create a group that will be considered unallied to any one nation but which will defend all nations from the threat of the Slada’sha. Due to Mouko’s inclusion, Muramasa pulls all ryuko support from this group and leaves the meeting – returning home. The group is called Dawnbringer and all present sign a pact to support its operations.A few months later, Leorajh arrives at the Isle of Dragons before everyone else to warn Muramasa. Mouko shows up and offers to rise the island so it won’t be destroyed. However, Muramasa throws them both out as he will not risk working with Mouko.
Mouko attempts to rise the island anyways but he doesn’t have enough time. The rising gigantic Slada’sha grabs the island with one claw and slams it back down into the ocean. The Isle of Dragons and some 80% of the ryuko people, are destroyed.
Mouko teleports to the Isle of Entropy and tries to save the land but it fails. With no other choice, Mouko explains his family that he can hold the Slada’sha in this region by using the fragmented buildings of the temple below to restrain it, but he cannot stop its minions and the infestation to come. It will spare them the main monster but not the waves of its creations. This will take everything Mouko has, so as a result he names Mizuki his replacement.
The next day, Muramasa tells his family he’s leaving. As the man single handedly responsible for killing 90% of his people in a single day, he feels unfit to be a part of the family or to wield its daisho. Besides, right now he wants to drunk till he’s stupid and hit something till he cannot feel – neither behavior will reflect well on the family. To help separate his identity from theirs (and thus not shame his family) he leaves behind everything that was his and takes on the name “Sensou”.
Sensou (Muramasa) drinks himself into a stupor. Ansel comes to see him, having talked to his family and learned of his decision. He tries and pull him out of it but it doesn’t work.
On Valentine’s Day no less, Clover finds Sensou (Muramasa) drinking himself silly and in no state to rule anything. He blames himself for the fate of his people, as do the survivors nearby, and she can do little for him. Worse, now that he has no entanglements to his people to hold him back she has entanglements to Ravenwood!