Although KT21 was a veteran Green Lantern, she had never intended to serve the Corps for so long. Like some fellow Lanterns, KT21 maintained a civilian identity on her home world Jerome.
KT21 was pregnant when she was inducted into the Corps, and has had to raise her son B.J. while acting as both a Green Lantern, single mother, and professional glass blower. Many years ago, the Guardians of the Universe promised KT21 that they would appoint a successor to Sector 181 when her son was born. They never commissioned a replacement, so KT21 learned to care for both her family and her Sector at the same time.
In her first apperance, KT21 is called away to apprehend a group of raiders who were working on behalf of the Warlord Poml. Trapped within a yellow containment bubble, KT21's air began to run out and her ring was powerless to break her free from the yellow prison.
The raiders left KT21 to suffocate but the Green Lantern quickly thought of a plan to escape. Before she left home, KT21 placed B.J.'s glass blowing toy in her pocket. Unlike her yellow prison, the red glass was not immune to her rings power. KT21 blew a huge red bubble inside of the yellow sphere she was trapped in, covering over the yellow glass with a red tint. KT21 blasted through the newly colored bubble and quickly rounded up the raiders before they could flee Jerome with their stolen goods.
KT21 would continue to serve the Corps during the multiversal Crisis on Infinite Earths. When the Crisis had passed, the Guardians of
the Universe were disturbed over their internal strife and failure to foresee the coming of the Anti-Monitor.
They decided to leave this plane of existence to meditate. Before doing so, the Guardians engineered a massive operation within the Corps to apprehend those criminals who had escaped from the Oan Sciencells during the Crisis.
KT21 partnered with Medyphll to capture
Plasma Fig, the villain who had murdered the Green Lantern Sandro Batorn. According to Plasma Fig, KT21 distracted the killer while the silent Medyphll snuck up and apprehended him. The two Lanterns deposited their prisoner back to the Sciencells, and joined the Corps gathering on Oa to mark the Guardians' journey.
Presumably, KT21 continued to serve the Corps through the first and second destruction of the Central Power Battery. When the Corps reformed, KT21 resumed her role as Green Lantern. She was on the front lines in the battle to stop Superboy Prime from destroying Oa, and fought in the Sinestro Corps War. When KT21 learned of the Sinestro Corps witch Kryb and her sick fascination with the children of Green Lanterns, she joined Amnee and Matoo Pree in their search for the monster. The trio were later joined by Kyle Rayner and Soranik Natu, who had uncovered a lead as to Kryb's whereabouts.
Kryb held her own against four Lanterns, but was eventually defeated. Although Rayner ordered his team to stay with Amnee, who was now in full labor, KT21 reasoned that the only way to protect their children was to make sure Kryb was dead. She lit her ring and raced off to aid Rayner in battle.
Together, KT21 and Rayner fought Kryb in a vicious battle. The alien witch was aware that Amnee was giving birth and the smell of the child drove her to fight on relentlessly. The Lanterns were aided by the unexpected arrival of the Star Sapphire, Miri Riam, who was alerted to the fact that a Sinestro Corps soldier was threatening a "great love." The added firepower she brought was just enough for the Lanterns to subdue Kryb.
While Kyle was preparing to transport Kryb to prison on Oa, KT21 vehemently protested, arguing that Kryb needed to be
put down for good. The children of Lanterns, like Amnee's newborn daughter and her own son, would never be safe as long as Kryb lived. Kyle refused, arguing that they were Corps and not executioners, but KT21 would not listen. She turned her ring on Kyle and Miri, blasting them away from their prisoner. KT21 then stood over Kryb and pressed her ring to the vile hags skull, intent on destroying her once and for all. KT21 was desperate and fearful for her son's safety, and Kryb took advantage of that fear to take the life of one more Green Lantern.
Without warning, the latice-like hump on Kryb's back opened up like the fingers on a clawed hand. These claws grabbed KT21, tearing her apart as she was pulled head-first into Kryb's hump. With a blast of his ring, Kyle quickly bound Kryb before she could escape, but the damage was done. KT21 was dead and her ring left her hand to find a replacement in Space Sector 181. Kyle constructed a coffin for KT21's body and transported the Fallen Lantern to Oa. There she would be entombed in the Crypts of Oa and honored alongside her fellow Corpsmen. The fate of KT21's son B.J. is unknown.