Tatsumaru, usually as seen in combat, draws his sword only against opponents he feels are highly skilled and worthy. When Shiunsai adopted Rikimaru & Ayame, Tatsumaru was somewhat of an example of what they were to strive at being. When Rikimaru was 18 Tatsumaru provided advice to his training before he attempted to pass the intiation that would pave his way into the Azuma clan. It can be strongly assumed that he was an Azuma ninja before Rikimaru or Ayame were. Now being an Azuma means one thing: shadow warrior. Tatsumaru has consistently expressed his knowledge in the advanced techniques of Azuma Shinobi-iri (silent movement & entry).
When Gohda Motohide rebelled for not gaining the title of daimyo and rulership over the country of Gohda, the Azuma were called to action to protect Lord Gohda Matsunoshin and the royal family. Before leaving the Azuma Village and departing for their mission, Master Shiunsai felt it was time to acknowledge his age, but more importantly Tatsumaru's skill and wisdom as an experienced Azuma Ninja. This was expressed by passing the ancestral sword "Izayoi" possessed & wielded by the Azuma Ninja Clan Master. Its symbolic meaning without being said, represented that he who possesses the sword is recognized as the Azuma Clan leader. Once the short ceremony was over, Rikimaru & Ayame recognized him as the Azuma leader and immediately headed for Gohda Castle. Upon hearing the situation from a servant, Tatsumaru proceeded with dispatching Ayame to save Lady Kei & princess Kiku while he and Rikimaru infiltrate further within and rescue Lord Gohda. As troops loyal to Motohide, aided by the Nyogetsu Ninja loyal to daimyo Yoshisada Toda killed servants and engaged in battle with Gohda samurai.
Tatsumaru and Rikimaru silently make their way through the carnage, swords clashed in the distant rain-filled night, the loud dying screams of warriors could be heard. In the midst of all this Tatsumaru senses a lone ninja within close proximity of their position. After sending Rikimaru alone to rescue Lord Gohda he decides to investigate the enemy ninja situation and then ascends to higher ground to further his search. Tatsumaru silently engaged samurai, using his Azuma training he sneaked behind enemies placing his hand over their mouth quickly drawing his sword and thrusting it into their chest silently performing the stealth kill.
Many samurai fell that night due to the newly appointed Azuma Master's ninjutsu skills. After ascending to what appeared to be a central high-rise section of the castle he came upon someone dressed as what appeared to be a kabuki or some kind of theatre dancer. Once the strange figure took notice to the Azuma Master's presence, they quickly rushed towards him and attempted to strike with an overhead cut with a full length katana.
Tatsumaru countered with an Azuma-taijutsu overhead block and an upward swipe from Izayoi cutting the disguise in half and revealing the identity of the wearer: Lady Kagami, Master of the Nyogetsu Ninja Clan that had served the House of Toda for generations. Possibly in her career she engaged in combat with Azuma Shiunsai or at least to some degree encountered Izayoi, because she instantly recognized Izayoi and commented with "And I recognize your sword, so old man Azuma finally retired" Lady Kagami. This shows that she knows whoever possesses the sword is the current Azuma Clan Master. After revealing her identity Tatsumaru saw it as an oppurtunity to end the war and rivalry between their two clans. Kagami attempted to reason with the Azuma Master by saying the two should unite and overthrow the samurai.
But the Azuma Master was reluctant and denied her request. She then called for Seiryu, a senior Nyogetsu Ninja. After a short battle on the rooftops Seiryu fell in battle to the superior combat skills of the Azuma Master. While standing on the edge Tatsumaru made a clean and quick sweep with Izayoi cutting the throat of the Nyogetsu Ninja and killing him before he even hit the ground.
After his battle he proceeded with checking upon Ayame's mission status. She reported Motohide had killed Lady Kei and kidnapped Princess Kiku and that she would pursue. Entering further into the castle he came upon the House of Gohda's senior advisor Sekiya Naotada and explainded the situation. Revealing that the Nyogetsu had infiltrated the castle already, in the midst of the conversation Tachibana Jubei reported that daimyo Yoshisada Toda was making his move and had massed his army at the border in preparation for all-out war. Upon hearing this, Tatsumaru leader of the Azuma Ninja willingly stepped forward to perform the assassination mission that would end the war before it began. Once sanctioned by Sekiya the Azuma Master sought out his target deep within his war camp. Upon arrival in the heavy rain soaked camp, Tatsumaru mentally prepared for a silent battle.
Drawing upon his Azuma training he knew visibility would be low and took full advantage of this performing multiple stealth kills while moving foward to the heart of the camp. He came upon the daimyo who quickly called for guards to aid and intervene. However, the Azuma Master's combat skills proved far more efficient than the samurais'. Killing both guards first, Tatsumaru engaged Toda finally, the samurai lord swung his enormous sword but his attempts proved to be in vain as the Azuma Master outmaneuvered him and blocked his attacks, following with quick combos of Azuma-taijutsu strikes that finally defeated him in battle. After the battle, Kagami proceeded with her plan of freedom by decapitating Toda and heading to a cliff edge to give the preset signal to attack his remaining forces. Kagami offered a second time to side with her and the newly born Burning Dawn. But the Azuma Master again refused and they engaged in a fierce battle of close combat. The duel ended in a draw when the cliff collapsed and both warriors fell into the sea.
After washing upon shore he was saved by Kagami. It quickly became clear he was suffering from a severe case of amnesia and so she took him back to the Kansen Caverns in order to recover from his injuries. After making a full recovery he was given the identity of the former Blue Dragon "Seiryu". The Burning Dawn four Lords were sent to a frontier town in order to kidnap villagers and use them as slaves to work on the massive warship, Fire Demon. Seiryu used his skills to quickly incapacitate the guards with fist strikes to the back of the neck knocking them unconscious.
After returning to the Caverns Kagami told him that the Azuma Ninja had discovered the Secret Harbor. His orders were to protect the slaves and eliminate any and all threats. While there Seiryu came upon Rikimaru, his former clan brother, silently attacking with a leading hop-kick of some kind. Rikimaru shifted his weight to the left avoiding the solid kick, Seiryu then immediately followed up with a high roundhouse kick. But Rikimaru was able to anticipate this and swiftly ducked the high attack. Countering as he rose with a horizontal swing of his sword aimed at his opponets head, but Seiryu ducked the attack, Rikimaru then quickly performed a vertical cutting motion from the ground up, but Seiryu quickly cartwheeled to safety preparing for the second stage of their duel. Seeking the identity of his enemy, Rikimaru asked who the masked enemy was. Seiryu drew his weapon which Rikimaru recognized as Izayoi the Azuma Clan sword.
After Seiryu removed his mask Rikimaru called him Tatsumaru, Seiryu commented that he was the Blue Dragon of the Burning Dawn. Seiryu then launched a swift uppercut strike with his sword, Rikimaru sidestepped and using his lead foot as leverage attempted a horizontal spinning attack. Rikimaru hastily raised his sword in defense and was pushed back. Both entered their stances and the duel was over. Angered by the discovery of the harbor Kagami sent Seiryu to attack the secret Quarantine Village near Gohda Castle.
His mission was to neutralize all the guards acting as security. Before leaving, Ayame approached him trying to remind him of his place with the Azuma Ninja. But she was attacked and Seiryu escaped but not before receiving strict orders to "burn the Azuma village to the ground" from Lady Kagami. Tatsumaru infiltrated the village along with Kagami and Burning Dawn Ninja and proceeded with his mission. Using his blowgun with great skill he killed a few Azuma Ninja this way. But his most common technique used on the elderly Azuma, was an Azuma-jutaijutsu technique. Silently approaching he grabbed his enemy, secured a firm grip then rolled backwards flipping the enemy onto their back then drawing Izayoi, the Blue Dragon finished them with a downward thrust to the throat. The blood of many fallen Azuma Ninja stained Izayoi, the spirit of the Azuma clan.
Seiryu made his way to the Azuma Master's house and entered. There he witnessed Lord Gohda and the old Azuma Ninja Master killing Burning Dawn Ninja. Lord Gohda rushed him but was stopped by a taijutsu fist strike to what appeared to have been his diaphragm because he immediately fell after the impact. Shiunsai then spoke of killing his father in the past and the two highly skilled ninja engaged one another. The old Grand Master proved a very worthy opponent using smoke bombs and shuriken along with his mastery over his cane sword. Using quick strikes and rapid slashes, but still it was no match in his advanced age for Tatsumaru's youthful and strong Azuma taijutsu which he taught him personally.
Tatsumaru killed Shiunsai with a thrust from the Azuma Ninja Clan sword Izayoi which he passed down to him. Rikimaru appeared shortly thereafter and they briefly dueled. Tatsumaru showed some signs of remorse toward killing the old man (Shiunsai's death marked the first sign of Tatsumaru's memory slightly returning) who taught him everything he knew about Ninjutsu. Rikimaru took advantage of his distracted clan brother and knocked him to the ground but his emotions clouded his judgement and, being the cunning ninja that he is, Tatsumaru reached for Izayoi and in one swift motion before Rikimaru could react, drew and swung Izayoi slashing the right side of his face and scarring him for life. Tatsumaru escaped with Kagami and were pursued by Ayame who helped him regain his memory but he chose to stay with the Burning Dawn. After launching the Fire Demon Tatsumaru stated why he chose to stay because he loved Kagami and then set off.
Killing all the Gohda Samurai onboard including Jubei, Tatsumaru engaged Ayame in a fierce one-on-one duel ending in a draw but stabbed himself with Izayoi as punishment for his crimes of treason. Even so he was still a highly respected Azuma Ninja who simply felt that ninja deserved recognition for their valiant acts, skills, and duties just as much as samurai did. This Azuma Ninja died believing that a worthy purpose in the highest regard but the method was wrong.
Tatsumaru returned in Tenchu Wrath of Heaven after being revived by Tenrai to serve as his servant although it is later revealed by Onikage that he had full control and eventually betrayed Tenrai to help the Azuma in both Rikimaru and Ayame's story. In Rikimarus story he appears at the Buddah temple where he slays Ganda before attacking Rikimaru, after their battle he reveals the secret to defeating Tenrai which was hidden in his right eye by their old master. Tenrai intervenes and is angered at his betrayal and extinguishes a candle which acts as a link to his life (each time a member of Tenrais army dies a candle is extinguished symbolising their life ending) and Tatsumaru falls to the ground dead much to Rikimarus dismay.
In Ayame's story Tatsumaru prevents the twin samurai Ukyo and Sakyo from killing Ayame with him later stating at Tenrai's fortress that it is his job to kill her. When Ayame reaches the Buddah temple to recover one of the three jewels she finds that Tatsumaru has been revived and already has posession of the jewel she seeks, Tatsumaru warns her that the next time they meet he will kill her without any hesitation. When Ayame reaches Tenrai's fortress she encounters Tatsumaru blocking her path and the pair fight with Ayame emerging the victor, Tatsumaru slumps to the ground wounded as Ayame rushes to his side telling him to hold on as she leaves to kill Tenrai with the following scene making it appear Tatsumaru has died from his injuries.
However it is later revealed to be false when he and Rikimaru both arrive to assist Ayame in the battle against Tenrai, Tatsumaru orders both Rikimaru and Ayame to escape and decides to atone for his past sins by leaping into the portal that Tenrai entered to revive Mei-Oh with a box of explosives.
There is also another story you can unlock by fighting Onikage in the other Castle. When Ayame reaches the end of Tenrai's fortress, Onikage will show up claiming to fight her. They fight and Ayame is the victor. But she ends up almost killed, until Tatsumaru appears. He blows himself and Onikage up to save Ayame.