"The Rusty Sword" (錆びた刀, Sabita Katana) is episode 231 of the Boruto: Naruto Next Generations anime.
Tsubaki dreams of training with Sazanka back in the Land of Iron. She wakes up wondering why she dreamed about that. Team 15 visits a merchant who was attacked by bandits in the hospital. He becomes distressed when hearing Tsubaki handle her sword, yelling that samurai are coming after him again. A nurse asks them to leave, and knowing that his assailant was a samurai, they start to investigate where he was attacked. They noticed cut bamboo, which Tsubaki determines was done by a skilled samurai. She recalls Sazanka's skill, and that the rumoured prize of a tournament was the right to claim Mifune's sword Kurosawa when he retires. Sazanka developed his skills to be worthy of wielding it one day. She recognises Sazanka's cut in the bamboo. Later at the Lightning Burger, Wasabi informs them there was another attack while they were investigating. Tsubaki shares her suspicion of who the culprit is. She reveals Sazanka was a genius of the sword, but abandoned the path he was on to pursue only strength, and was caught trying to steal Kurosawa, and killed his fellow disciples to get away. Tsubaki assures them she will have no problem fighting him, and practises at night.
The next day, Team 15 lays a trap, attracting the bandits' attention. Most of them get caught, but they hired Sazanka as protection. Tsubaki comments on how he's changed. He says he forgot to kill her. Sazanka draws his sword, and cuts Tsubaki, who hasn't drawn hers. He dodges Namida's attack, and Team 15 retreats. Wasabi treats Tsubaki, asking why she didn't draw her sword. She asks to be dropped from the mission, and reveals she blames herself why Sazanka turned out the way he did. She won the tournament by chance, and that started to change him on who he is today. Wasabi tells her they might capture him if they ask for reinforcements, but warns her that her regret will continue to grow if she doesn't deal with Sazanka herself. Namida and Wasabi point out how she has grown and changed since coming to Konoha, restoring her fighting spirit. Sazanka tells the bandits there's something more important than money he has to do. Team 15 attacks them, Tsubaki going to deal with Sazanka. Sazanka believes that a sword's purpose is to cut, so he has cut many people since the Land of Iron has pursued him, and deems that whatever Tsubaki has done since isn't real training. He says he has given up on Kurosawa because he has acquired power, and charges at her. They cross swords, and noticing there are no openings in his attack, she performs her Secret Sword: Snowstorm Beheading. He cuts through it. He recalls when she won against him, and now wants her to admit defeat. She refuses, and refutes his claims against her, saying she has gained strength from the friends who trust her. They cross swords again, and Tsubaki cuts him down. She is saddened by having to do it in these circumstances. Sazanka acknowledges her strength. Later, Wasabi and Namida help her around. They laugh as Tsubaki teases them, saying they should pay her more respect.
|Tsubaki Kurogane||Juri Nagatsuma||長妻 樹里||Nagatsuma Juri|
|Wasabi Izuno||Natsumi Yamada||山田 奈都美||Yamada Natsumi|
|Namida Suzumeno||Sara Matsumoto||松本 沙羅||Matsumoto Sara|
|Sazanka||Chado Horii||茶渡 堀井||Horii Chado|
|Bandit leader||Kosuke Katayama||片山 公輔||Katayama Kōsuke|
|Bandit||Kazuya Saji||佐治 和也||Saji Kazuya|
|Samurai referee||Hirokazu Sekido||関戸 博一||Sekido Hirokazu|
|Merchant||Ryo Nishitani||西谷 亮||Nishitani Ryō|
|Nurse||Kumi Takaragi||宝木 久美||Takaragi Kumi|