In dragon quest V how do you save your wife?

In Dragon Quest V, to save your wife, Bianca, you need to defeat the game's final boss, the Overlord, in the final chapter. After your initial confrontation with the Overlord, you'll have the opportunity to rescue Bianca from his clutches. Once you defeat him and complete the necessary events, you will reunite with her, and she will join your party. Completing this sequence of events allows you to save her and ensures a happy ending.