Date Masamune

Bontenmaru is the future Date Masamune(伊達正胸) and a christian samurai.

Appearance
Bontenmaru has blonde hair and heterocromatic eyes, one chestnut, the other blood red, which causes her to wear an eyepatch due to people calling her a demon child. she tends to wear black clothes with christian adornments. Finally, it has been noted that she is both asian and not, a mixed ancestry which is not exactly unnoticed by her peers.

Personality
Bontenmaru very much seems to value christianity, but she values it most because she believes herself to be the beast spoken of in revelations himself in human form, in other words she happily expresses, with 8th grader syndrome and a whole lot of over the top whackiness to boot, that she will eventually destroy the entire world.

However, she really is just a hyperactive child seeking some form of love and attention which she is unfortunately deprived off often and made fun off for her eyes and racial type.

Due to her 8th grader syndrome she seems to believe she can summon demons and form seals and barriers, despite the clear reality. Yoshiharu describes her as the perfect "Jakigan" character, and ultimately, due to explaining to her how she can use her Heterchomia to scare off her enemies, he ends up inspiring her, unintentionally and without even realising who she is, to usurp the throne of Oshu, take over Japan and join the Nanban to sink the country to the bottom of the ocean as the beast of revelation should.

She seems to look up to Yoshiharu, who can reason with her very well at times, and admires Nobuna, due to the similar backgrounds they bare. When it comes down to it, half of her actions thus far have actually been encouraged by Yoshiharu's words and her own ambitions or delusions.

Background
Her mother was said to have had an affair with an unnamed foreigner, which led to Bontenmaru's birth and subsequently the tension between her parents. Her brother is the favourite while she is percieved as evidence of her mother's affair.

Because of her eyes, her people began to believe she was punished by the Buddah due to her birth, and half banished her to Sakai, even her own mother seemed to find her eyes hard to look at, calling them ugly.

Her Aide since young is Katakura Kojuurou.

Kyoto Arc
She first appears when Yoshiharu enters a christian church, at which point she attempts to keep him out using a seal, which obviously doesn't work. When she tries to draw her sword, she is stopped by Louise Frois, who asks her not to be rude to those who come to hear the words of their god, Bontenmaru submits, but continues to complain to Yoshiharu until he ends up picking her up and treating her rather comically like a child. After Yoshiharu encourages her and tells her the truth about her Heterochromia and calls her a "jakigan" character, she ends up becoming inspired by him and decides to use her "jakigan" to conquer Oshu. Shocked, Yoshiharu asks who she is and she calls herself Date Masamune before running off to usurp the throne, conquer Oshu and take over the entire country thus leaving Yoshiharu to contemplate the consequences of what he has just done.

Retreat at Kanegasaki Arc
Back in Oshu, Bontenmaru builds an anti-christ church and summons her aide Katakura Kojuurou. She declares that she will take up the name "Jakigan Masamune", noting how Yoshiharu said her eyes were popular in the future, and decides to overthrow her father, take over the surrounding territories and dominate her way straight into Kyoto, where she will duel Nobuna to see who the real demon lord is. Half terrified, half confused, Kojuurou ends up dragged into it behind her master.

Sagara Yoshiharu
Like with most children Yoshiharu is kind to Bontenmaru, even letting her on his lap and shoulders after their first meeting. He acts somewhat like an older brother to her. When he mentions that mixed racial children like her are more common in his time she begins to confide in him due to her situation and ultimately grows to admire Nobuna when Yoshiharu tells her about their similar situation. She got the idea of her "Jakigan" from him after he mentioned it and revealed to her the truth of her Heterochromatic eyes, and shockingly puts it to genuinely good use in psychological warfare later on. When he realizes that she is Date Masamune, he is both confused and horrified since he has literally just taught her how to use her heterochromia to defeat the superstitious individuals of the modern age. Essentially, when he hears Bontenmaru loudly declare she will use what he taught her to usurp the throne, conquer Oshu, unite with the Nanban people and sink all of japan as the beast of revelations, his only response possible was to ponder the consequences of what he had just unleashed upon the world. Later, on Yoshiharu even has to stop her rampage due to Oda needing the aid of Takeda Shingen and Kai, who Bontenmaru had actually managed to put into a tight spot, he's stopped by the arrival of Magoechi Saika, who Bontenmaru was smart enough to employ, but ultimately his life is not harmed and he is able to talk Bontenmaru into going home to aid her mother who's fighting her uncle. At this point in the story, he still acts like an older brother to her, scolding her for her actions yet also giving her good advice and encouraging her to help the mother she is afraid will turn on her, due to her insecurities about her eyes and mixed racial birth. Being the only man who actually knows what her "Jakigan" really is, just a harmless pair of different colored eyes, Yoshiharu is probably also one of the few people who actually would fight her in battle, everyone else is too afraid of the rumors spread by her herself about the eye's so called supernatural powers.

Oda Nobuna
Although they have only met once, Date Masamune and Oda Nobuna have an interesting set of parallels between oneanother, as Yoshiharu pointed out. Both have strong connections to the Nanban people, and both have poor, at best, relationships with their mothers. Date also seems to see Nobuna as her potential rival, as she believes herself to be the beast of the bible and wants to fight Nobuna, the Demon King of the Sixth Heaven. Both of them are also very close to Yoshiharu, albeit in different ways, and he is the one who influences them the most out of others alive at the present time.