Jamie Osen began her adventuring career as a mage in the A-rank party Thunder Pike, driven by the urgent need for funds to buy medicine for her critically ill younger brother, Tac. Within Thunder Pike, she endured mistreatment from leader Simon Barkley and teammates Barry and Camilla, facing bullying and peer pressure that forced her into participating in the abuse of fellow member Yuke Feldio. She privately regretted these actions, maintaining a moral compass distinct from her party.

Following Yuke's departure, Thunder Pike's effectiveness plummeted. Simon escalated to criminal activities, conspiring with corrupt official Besio Salas to blackmail Yuke and enslave members of his new party, Clover. Jamie secretly recorded evidence of these schemes. During a confrontation in the Achromatic Darkness dungeon, she betrayed Thunder Pike, using magic to save Clover from a collapsing floor, freeing them from restraints, and physically stopping Simon from taking Rain hostage. This left Thunder Pike facing a horde of orcs; Barry and Camilla perished. Jamie escaped but Simon, transformed into an undead by a cursed artifact, severely injured her.

Rescued by Clover, Jamie faced legal consequences as Thunder Pike's sole survivor. Her cooperation in providing evidence against her former party and Besio, plus her lack of involvement in their racist actions, earned her a reduced sentence: a one-year suspension from adventuring instead of harsher penalties. During suspension, she worked as an Adventurer's Guild receptionist to repay societal debts and support Tac. Yuke later provided the medicine that cured Tac, lifting her financial burden. The king eventually pardoned her suspension early due to her heroic actions.

Jamie officially joined Clover. She formed bonds with members Marina, Silk, Rain, and Nene and actively sought redemption, apologizing to Yuke for not defending him during their Thunder Pike tenure. She transitioned from offensive magic to awakening as a Red Mage, aligning her capabilities with Yuke's support-oriented class as an expression of admiration and commitment.

Physically, Jamie has blonde hair typically tied in twin-tails with ribbons, green eyes, freckles, and a noticeably curvaceous figure. She originally wore a purple adventuring dress with black gloves, stockings, and heels. After joining Clover, she adopted a red-themed uniform with yellow bows and fur trim. Her casual wear included a lilac sweater with a skirt or pants.

Personality-wise, Jamie exhibited kindness and moral conflict even during her Thunder Pike membership. Post-redemption, she expressed genuine remorse for her past compliance and demonstrated eagerness to contribute positively to Clover. She possesses notably low alcohol tolerance, leading to uninhibited behavior like kissing party members and attempting to seduce Yuke while intoxicated, followed by sincere apologies. She maintained persistent romantic feelings for Yuke, confessing while drunk and later attempting to advance their connection sober.