Ike assumes leadership of the Greil Mercenaries after his father is killed by the Black Knight. And most of the time, he is in the service of Princess Elincia, serving as her personal bodyguard.

Ike is introduced as the newest member of the Greil Mercenaries, and after Ike assumes leadership of the Greil Mercenaries after his father is killed by the Black Knight. A number of the other members, including the likes of Boyd (who considers Ike a rival and enjoys poking fun at him) and Shinon (who is genuinely antagonistic), look down on him as a rookie, constantly mocking his inexperience and flouting their skills. As news of Daein's invasion eventually reaches Greil's ears, Ike is pushed into working twice as hard in order to ensure that he is well prepared to take over the reins of the company. Following Greil's death, Ike takes over the leadership of the Greil Mercenaries, much to the disbelief of Gatrie and Shinon. The pair then proceed to leave the Greil Mercenaries, as their immense pride restricts them from serving under an individual whom they consider to be inferior to them. After remaining in Gallia, Ike comes to the realization that Caineghis is unable to help him. He then leaves the country, and is escorted to Port Toha by a squad of Laguz, comprising of Ranulf, Lethe and Mordecai. With the assistance of his growing band of mercenaries, Ike travels around the continent of Tellius, helping Elincia reclaim her home kingdom of Crimea. To this end, he eventually gains the support of Empress Sanaki of Begnion in overthrowing Daein, becoming the leader of the newly formed Crimean Liberation Army.

As the war nears its conclusion, Ike reveals the Divine Blade Ragnell, admitting that he has been keeping it ever since the night Greil was slain. With the blade in hand, Ike challenges the Black Knight to a duel in a tower of Nados Castle with the assistance of Mist. This battle concludes with the tower being destroyed and the Black Knight declared dead.

Ike eventually succeeds in defeating Mad King Ashnard of Daein, reclaiming Crimea from Daein's grasp, and allowing Elincia to rise to the Crimean throne, becoming known as the “Patriotic Hero.” In the aftermath of the war, the new Queen Elincia granted Ike a court title and land in recognition of his distinguished service. However, he disliked being caught up in the politics and in-fighting between the other nobles and renounced his title to return to a life of simplicity with the other mercenaries. Soon after this, he was contacted by Bastian, the Count of Fayre, about rumors of a rebellion against Queen Elincia. Bastian had told him that in preparation to counter this with an ambush, Ike and his crew would have to seemingly abandon their homeland of Crimea and go into hiding. Soon after, he leads the Greil Mercenaries into interrupting Lucia's execution.

Upon returning to the headquarters of the mercenaries, Ike is visited by Ranulf, who provides news of an oncoming war being waged by the newly formed Laguz Alliance and Begnion. It is then revealed that the flames of ire among the alliance sparked as a result of the countries involved learning of Begnion ordering the extermination of the Herons in the distant past. Despite being reluctant to join the conflict at first, Ike eventually agrees to lend his mercenaries' military expertise to the alliance.

The conflict between the alliance and Begnion eventually escalates to a breaking point, whereupon Ashera is interrupted from her thousand-year slumber. She then passes her judgment upon the continent of Tellius, turning practically everyone, save for the strongest warriors in both armies, to stone. The Goddess of Chaos, Yune, then breaks free of her shackles within Lehran's Medallion, and possesses Micaiah as a means to communicate with others, apart from Micaiah herself. This essentially leads to Ike forming a truce with Micaiah's forces, as they traverse toward the Tower of Guidance.

While progressing through the levels of the Tower of Guidance, Ike encounters the Black Knight, and finally avenges his father's death by defeating him in a true one-on-one duel. At his opponent lies dying, Ike shows a deep sense of gratitude, admitting that while Zelgius was his enemy and father’s killer, he was also a teacher of sorts who guided him. He recognized that his skill with a blade was rugged and unpolished right after he lost his father, and it was only through his countless clashes with the Black Knight that he was able to polish his skills and the secret art of “Aether.” Upon the Black Knight's passing, Ike takes possession of Alondite, the sister sword of Ragnell.

It is revealed that Ike bore witness to Greil's accidental murder of Elena. In a bid to eliminate the immense trauma that Ike was forced to face as a result, Sephiran sealed his memories of the scene. All of Ike’s memories surrounding that event –including when he met Soren –were buried deep down as a result. After regaining his memories, Ike comes to finally understand just why Soren had trusted him so much and remained by his side through thick and thin.

After countless fierce battles, Yune blessed Ike with her divine power –which is where he truly ascends to become The Radiant Hero. When it was all over, he disappeared, leaving the continent of Tellius without a trace and becoming a legend, being known throughout the world as both a great warrior and a great man.