Fin first appears in Fire Emblem: Seisen No Keifu as a young Lance Knight following the prince of Lenster, Cuan and his wife Ethlin as they come to Sigurd's aid in the first chapter of the game. Cuan and Ethlin later leave Sigurd's army in order to check up on their own kingdom and Fin returns along with them. In the final chapter of Sigurd's story when Cuan and Ethlin return to help him once again with a much bigger force behind them, Fin remains at their home castle in Lenster to guard the king and Cuan's son, Leaf. Fin is not around to watch Cuan and Ethlin die at the hands of Trabant and his dragon knights and is also no longer a part of Sigurd's army when they are ambushed by Alvis. When the empire comes to claim Lenster Fin escapes the castle with Leaf and disappears into the wilderness with the child prince.
During this time Fin spends most of his time on the run from the empire along with prince Leaf. At some point he picks up Nanna, the daughter or princess Lachesis of Nodion and raises her as his own daughter. Fin acts as Leaf's closest bodyguard and advisor during his rebellion against the empire, protecting both him and Nanna during this time. Leaf later joins up with Celice, the son of Sigurd and Diadora, as Celice becomes the overall commander of the rebel army Fin then becomes the only character to serve under every lord in the Jugdral storyline. Fin continues service under Celice until the rebel army defeats Yurius in the final battle and reclaims the capital of Barhara. After the final conflict, Fin returns to Lenster with Leaf and Nanna to rebuild the kingdom.