Rio, born an orphan in Beltrum Kingdom's slums, is the son of Karasuki Kingdom immigrants Zen and Ayame. Witnessing his mother's murder by adventurer Lucius Orgueil at age five cemented his life in the slums and fueled revenge. At age seven, he regained memories of his past life as Amakawa Haruto, a 20-year-old Japanese university student who died in a bus accident. These memories merged with Rio's consciousness, forming a unified identity viewing itself primarily as Rio, incorporating Haruto's knowledge, skills, and moral framework. Haruto's past life involved extensive martial arts training (Chinese kenpo, jiujitsu, and other styles), swordsmanship, and academic achievement. He deeply regretted never reuniting with his childhood friend and love interest, Ayase Miharu, before death, a regret influencing Rio's relationships and actions. After regaining these memories, Rio saved Princess Flora Beltrum from kidnappers, leading to enrollment in Beltrum Royal Academy as a reward. There, he faced commoner-status discrimination, with Celia Claire as his sole ally and teacher. A false accusation of attempting to assassinate Flora forced him to flee before graduation. Seeking roots and stability, Rio traveled to the Yagumo region. He discovered his royal lineage as the grandson of Karasuki Kingdom's ruler, connecting with his grandparents and cousin. He trained with the spirit folk (Seirei no Tami), mastering spirit arts and forming a spirit contract with Aishia, a high-ranked humanoid spirit residing within his soul. He later returned to the Strahl region using the alias "Haruto Amakawa" to avoid recognition as a fugitive, employing a magical artifact to change his distinctive black hair to gray. Rio possesses abilities stemming from both lives and his true nature as the reincarnation of the Dragon King (Ryuo). His combat skills include mastery of "Ancient Martial Arts" from Haruto's memories and advanced swordsmanship developed at the academy and beyond, enabling him to defeat elite knights and rival heroes. He wields spirit arts, allowing manipulation of all elements, healing, body strengthening, and hypnosis without a formal spirit contract initially. His contract with Aishia evolved into a Spirit Pact, enabling spirit assimilation—merging their beings into a single entity with enhanced capabilities and access to Spirit Arms (materialized soul weapons). He possesses limitless magic essence (odo), recognized as bottomless. He holds the transcendent Divine Authority "Annihilation," granted by the world's true god, allowing him to nullify or erase anything he fully perceives, first used against the Great Spirit of Earth. His equipment includes a mithril sword (later destroyed), black wyvern leather armor (repaired and modified over time), a space-time cache for storage, a color-changing artifact for disguise, and a portable rock house with Japanese-style amenities. After spirit assimilation with Aishia (Volume 20), his hair turned white, his eyes crimson, and his scars healed completely. Personality-wise, Rio is calm, rational, analytical, and exceptionally humble, often acting reserved to avoid attention. He prioritizes protecting friends but struggles with feelings of unworthiness for happiness due to vengeful goals, particularly regarding Miharu. He exhibits ruthless protectiveness when allies are harmed. His development shows gradual acceptance of relationships and bonds, influenced by figures like Celia and Aishia, moving from isolation toward valuing familial connections by Volume 16. He grapples with moral dilemmas, shifting from rigid non-lethal stances (influenced by Haruto's ethics) to accepting necessary violence after nearly killing an assailant attempting rape. Key relationships define his journey. Celia Claire offered kindness at the academy, becoming a trusted confidante; he later rescues her from a forced marriage. Aishia, his contracted spirit and Lina's divine creation, provides emotional and physical support, sharing a profound bond enabling fusion. Latifa (reincarnation of Suzune Endo, who died in the same accident as Haruto) started as an assassin sent to kill him but became his adopted sister after he freed her from magical enslavement; she harbors romantic feelings. Miharu Ayase, Haruto's childhood love, is recognized by Rio; he initially avoids involving her due to guilt and identity conflicts, but she learns his true identity through Aishia and actively pursues a relationship. Liselotte Cretia (reincarnation of Rikka Minamoto, another bus accident victim) is a noble and businesswoman who deduces Rio's identity; they develop mutual trust and a casual relationship after revealing their reincarnation origins. Princess Flora Beltrum admires him and recognizes him despite his disguise, while Princess Christina Beltrum initially distrusted him but later seeks his help and confirms his identity. Rio's transcendent nature was recognized by the World during the invasion led by Saint Erika, revealing a 1000-year plan orchestrated by Lina. He gradually learns about his original life as the Dragon King and the Divine Rules restricting his interactions. This journey involves settling inner turmoil, confronting Lucius for revenge, protecting allies across regions, and navigating complex political conflicts while uncovering deeper truths about his existence and purpose.