Tatsu Yamashiro is one of the former handlers of Oliver Queen. Tatsu is also the wife of the late Maseo Yamashiro, and the mother of the late Akio Yamashiro. She later became a guardian of the Lotus as part of the Crescent Order.
Housing Oliver Queen
Some days later, Oliver asked where Tatsu was where Oliver stated that she disliked him. Maseo corrected Oliver that Tatsu hated Oliver.
A while later, Tatsu told Maseo that she just wanted to go home but was told they can once they deal with Chien Na Wei. After Oliver was interacting with her son, Tatsu demanded Oliver to stay away from him. She proceeded to give him a meditation that helped Oliver remember where he saw the man hide the envelope. After Oliver thanked her for helping him remember, Tatsu demanded that Oliver leave their home as soon as possible.
After Oliver left his dirty clothes, Tatsu reminded Oliver that she isn't his mother or wife and told him to do his own laundry. Hours later, Tatsu worried something had gone wrong as Maseo said he should only take an hour. Tatsu calls a friend to watch over Akio while she left with Oliver to search for Maseo. When they arrive at the docks, they meet the triad. After Oliver attempted to greet them, Tatsu rescued Oliver, using her Katana. Tatsu asked one of the men what happened, where she was told that they killed three A.R.G.U.S. agents. When Tatsu arrived home, she was shocked seeing her husband alive.
Oliver and her husband began capturing triad members and torture them for information. After they kidnapped a man that stole the Omega virus, Chien Na Wei tracked down the house of Maseo. Chien broke into her home and confronted Tatsu and her son. Tatsu told Akio to run, however, Chien blocked the way and picked up one of the swords. Tatsu threw a chair and grabbed a sword after which she fought Chien in a sword fight. Tatsu got injured and lost against Chien who took her away.
Maseo and Oliver go to meet with Chien to trade the Omega virus for Tatsu. However, Amanda Waller anticipated that they would hand over the virus and swapped it for a fake, which Chien found out, forcing the trio to fight their way out. They managed to get away successfully and Tatsu was reunited with Akio.
After the conflict was done, the Yamashiros and Oliver planned to return to Japan. Tatsu, no longer hating Oliver due to his role in saving her life, offered to continue to provide housing for Oliver until he returned. However, the four were ambushed by Shrieve's men.
War with the League of Assassins
After Oliver losing his death match against Ra's al Ghul, Maseo secretly took Oliver's unconscious body to Tatsu for her to heal him.
Because Ra's planned on unleashing the Alpha-Omega on Starling City, Oliver told Malcolm to recruit Tatsu in stopping him. Upon meeting John, Felicty, and Laurel, they didn't trust her nor believe Malcolm. It was until Tatsu told Felicity about her past that caused then to have no choice but to go to Nanda Parbat. As the League surrounded them, Tatsu was forced to battle her husband. In the end, Tatsu killed Maseo and sang a song while crying. Tatsu and Team Arrow were eventually surrounded and they were all captured. Before Ra's al Ghul locked the team in a room with the Alpha-Omega virus, Tatsu was transported to another room as she had been inoculated years ago.
In early 2016, Nyssa al Ghul and Talibah confronted Tatsu in Kyushu, attempting to take the Lotus. Tatsu denied Nyssa's request as it was her responsibility to protect the elixir. Nyssa and Tatsu engaged in a sword fight, but eventually found their skills to be too evenly matched for an outcome. Nyssa then gave Tatsu the option to keep fighting until one of them drops from exhaustion or give up and listen to what she had to say on an issue concerning Oliver. Upon the mention of Oliver, Tatsu agreed to listen.
Nyssa explained that Oliver's sister Thea needed the Lotus as she was dying from her bloodlust. Tatsu then willingly gave her the Lotus to save Thea's life.
It was stated that Tatsu hated Oliver. She did not hide this either when she openly told Oliver he can thank her for helping him with his tasks by disassociating himself with her family once his job was done, unaware that Oliver was only helping Amanda Waller to safeguard her and her family. She later warmed up a bit to Oliver as he confronted Chinese Triad members in an attempt to find Maseo. After Oliver played a vital role in saving her life and stopping the Omega weapon, Tatsu's opinion of Oliver changed completely, even offering to stay with their family in Japan for a couple days so he can relax before returning to Starling City.
She deeply cares for her son and husband and this might be the reason for her hostile stance towards outsiders.
Upon, reuniting with Oliver five years later, Tatsu now consider Oliver a friend as she addressed him by his name, something she never once did when she hated him, in the present day, although she still loves Maseo, Tatsu is estranged from him, due to him being a member of the League of Assassins.
- Master combatant/Martial artist: Tatsu is extremely skilled in close quarters combat and martial arts, as she was able to defeat many members of the League of Assassins and hold her own against Maseo Yamashiro for quite some time before being beaten. Over the years she spent as a member of the Crescent Order, Tatsu became skilled enough to fight on par with Nyssa al Ghul.
- Master swordswoman: Tatsu is highly skilled in swordsmanship. She cut down multiple Shu gang members in mere seconds and was able to hold her own for a while against Chien Na Wei. Tatsu could also easily defeat many members of the League of Assassins by herself and beat Maseo in a sword fight. After recovering from his duel with Ra's al Ghul, Oliver Queen asked Tatsu to train him in sword fighting, showing that he respected her skill with the weapon. Since becoming a member of the Crescent Order, Tatsu's abilities as a swordswoman have greatly improved, allowing her to duel evenly with Nyssa al Ghul.
- Expert knife wielder: Tatsu was able to kill member of the Triad by throwing a knife at him.
- Medical knowledge: Tatsu has displayed a masterful level of knowledge and expertise when it comes to using herbs as alternative medicine, so much so that she was able to heal Oliver back to life after he suffered a fatal wound at the hands of Ra's al Ghul.
- Meditation: Tatsu is skilled in meditation and was able to guide Oliver into using it to analyze his memories.
- Multilingual: As a native Japanese, Tatsu speaks that language fluently, in addition to Chinese and English.
- Yamashiro family katana: Tatsu can proficiently wield a katana that was passed down through Yamashiro family and was once wielded by Ichiro Yamashiro and Masako Yamashiro.
- Suit: Tatsu wears a protective suit, as her heroine alter-ego to hide her identity from her enemies. It is unknown what materials it's made out of.
- The role was originally to be played by Devon Aoki but due to other commitments, Rila Fukushima was cast for the role.
- In DC comics, Tatsu Yamashiro is a heroine known as Katana. In the Prime Earth continuity, she wears the same outfit as seen in Arrow. Katana was originally associated with Batman as part of his superhero team The Outsiders. Also, in the comics, she is the wife of late Maseo Yamashiro (who was killed by his brother Takeo) and she has two children, Yuki and Reiko. Her sword is Soultaker, in which Tatsu captures the spirits of those who are killed and communicates with souls of deceased relatives and her husband.
- Although Tatsu sports her vigilante outfit from the comics, she is only referred to as "Katana" in concept art and merchandise, but never on screen.
- Tatsu was Oliver Queen's fifth mentor, after her husband, Maseo.