During the events of Genealogy of the Holy War, the Forseti tome first appears after Sigurd's troops reclaim Silesse Castle from Daccar's grip in Chapter 4. Lewyn, worrying for his mother's safety, enters the castle to reunite with her. There, evidently moved by Lewyn's display of maturity, Queen Rahna decides to entrust the tome of Forseti into his possession, urging him to use its power for peace.
The events of the Battle of Barhara that occur in Chapter 5 see Lewyn perishing, only to be resurrected by the spirit of the Wind Crusader Forseti residing within the tome. The tome is then inherited by Lewyn's son, while the soul of Forseti continues to inhabit Lewyn's body throughout the events of the second generation.
During the events of Thracia 776, the Forseti tome is the weapon of choice wielded by Ced, who directs its powers towards commanding the Magi Squad, a rebel group motivated by a desire to purge the Loptyr Sect's influence from Manster.