X Reader is a term used in secondary creations known as “Yumehon” in Japan. It's a creative genre that depicts interactions between copyrighted characters from manga or games and original characters prepared by the reader (writer).

Depending on the writer, the relationship can vary, such as being depicted as a friendship with an original character or a work depicting a romantic relationship. By introducing original characters that do not originally appear in the work, it is a popular creative genre that can express personalities and behaviors that copyrighted characters do not usually show, without changing the relationship with other copyrighted characters in the same work.

Touken Ranbu is a game set in a future world where beings, known as Saniwa, who can manifest the souls dwelling in objects, time-travel back to the past to battle entities attempting to alter history.

Players become such Saniwa, and fight alongside the souls embodied in swords and spears. The basic definition of a Saniwa is 'a being that can manifest the souls residing in objects', and thus, any being that can exercise this power, regardless of their gender or whether they're a cat, a dog, or a hamster, can become a Saniwa.

In the past, an anime adaptation depicted a Saniwa that appeared to be a young boy, whose gender was not specified, in consideration of all the game players.

Tsurumaru Kuninaga is a sword-warrior of the longsword.

Believed to be a sword forged during the Heian period, he is depicted as youthful-looking but often acts and speaks more maturely than other characters.

In line with his words to the player, 'A blade's life (human life) needs surprises. If it's only events that can be predicted, the heart dies first,' he is always surprising someone (at the level of a child's prank), launching surprise attacks on enemies, and keeping his own heart excited.
Having spent an incredibly long time as a sword without decaying and changing owners frequently, he has developed a dislike for 'boredom'.

He loves to surprise others, but he also loves being surprised. He can be described as mischievous, with the appearance of a mature-looking young man.

Mikazuki Munechika is a longsword-wielding sword-warrior.

He is one of the “Five Great Swords,” considered among the five most beautiful blades in Japanese history, and is said to be the most beautiful of them. Like the previously mentioned Tsurumaru, he is believed to have been forged during the Heian period.

His personality is dignified, elegant, and graceful, much like a nobleman. While that might sound cool, he has a tremendous pace and is unflappable in most situations. Therefore, even in tense scenes, he often stands firm and confident, which makes him quite reliable.

He's been in the game since its initial release, and as the highest rarity character in Touken Ranbu, he's often treated as a main character in various media (anime, manga, games, exhibitions), and has a high degree of recognition.

Heshikiri Hasebe is a Uchigatana-wielding sword-warrior.

When introducing himself, he asks the Saniwa to call him 'Hasebe.' This is because his former master, Oda Nobunaga, caused a great deal of trouble using Heshikiri Hasebe, and then passed him on to a person who was not even a retainer. As a result, he has a bit of a complex about his name.

His personality is quite competitive and sarcastic. However, he speaks politely to the player, the Saniwa, and is loyal and obedient. It's not that he's ingratiating himself, but he has a strong desire to be recognized by the player for his competence and ability to do his job well. He seems to believe that if he is recognized as a competent individual, he will never again be passed on to someone else.