Tanimoto Kaede was the younger sister of Tanimoto Natsu, a former member of Ragnarok's Six Fists. Kaede and Natsu were orphans until they were adopted by a wealthy businessman. Natsu worked tirelessly to become the perfect heir for his stepfather, driven by the need to care for his sister, who suffered from a life-threatening illness. When their stepfather finally took Kaede to one of his medical facilities, he fell in love with a female doctor there and married her. For a short while, the family of four experienced happiness, even seeing genuine smiles from the stepfather. However, this tranquility was fleeting, as the stepfather was found dead one morning, with no clear cause determined by the police. The authorities quickly suspected the stepmother, taking her away and leaving Natsu to manage the company alone.
Sometime later, Natsu discovered that the stepmother had never properly treated Kaede's illness, causing her condition to deteriorate. As she lay dying, Kaede's final words to her brother were a plea for him never to give up. These words, combined with the possible deception of his stepmother and his rescue from Hondo by Ogata Isshinsai, drastically changed Natsu's once innocent personality. This transformation, along with the rigorous training under his master Ma Sougetsu, turned him into a cold, ill-tempered individual. Later, when Natsu met Shirahama Honoka, he saw many similarities between her and his late sister, leading to a sibling-like relationship despite Honoka's clumsiness and childish behavior often irritating him.
Kaede's last words also instilled in Natsu an unyielding determination never to lose a fight, which fueled his motivation during his second battle with Honoka's brother, Kenichi, and later in his deadly match with Chou Enshin. Her memory served as both a driving force and a haunting reminder of the past he could never escape.
