After a long and fulfilling life, a man who has accomplished much, traveling the world, learning several languages, and even reaching a level of mastery in a historically preserved version of the Japanese art of Taijutsu as it was practiced by the ancient Samurai and Ninja before finally being lead by the spirit of mastering one's own body in order to protect and help others driving him to become a medical practitioner and going into nursing school before finally settling down in his old age to focus on his medical career and to help his children raise his grankids . On one day, he was asked by his son to babysit. But, when he decided to take his granddaughter for some ice cream the unthinkable happened.
A massive 17 car pile-up. The air-bags deployed in time to save him from any serious harm, but his precious granddaughter who he had carelessly allowed to ride in the front seat due to the lack of a proper car-seat had not fared so well. As she was hovering on the brink of death, a voice spoke to him. This voice that called itself a goddess promised that he could take the consequences of his mistake entirely onto himself in order to save his precious granddaughter's life. In exchange, all he had to do was remain in a deep state of meditation, using the unique meditation he had developed as part of his combat style. This goddess claimed that his meditation was truly unique, and it had the power to give her what she needed, a chance to leave this world from which a weakened goddess such as herself was incapable of leaving on her own.
For any other reason, he would have never listened to these words, seeing them as the voice of a demon. However, if it was to save his granddaughter, he would gladly sell his sole to this demon. He did exactly as she said. The last thing he remembered before dying of the injuries he had transferred to himself from his granddaughter was that same granddaughter's worried voice calling out for him. The next thing he remembered after that was waking up in the womb, having been reincarnated. Soon after this, he discovered that he was sharing this space with someone else. He had heard of reincarnation, but never dreamed he would be reborn with all his memories, and even less so that he would be reborn as the sister to the very goddess who had helped him save his granddaughter.