We returned to the Tower in a swirl of the Traveler's power. One moment we were inside the Traveler, and the next, we were inside the quarantine box, beside Kari's bed.

Her blackened limbs were tied down. She fought the restraints until the bed rocked. One of her eyes glowed a sick Hive green. As we entered, she ceased struggling and gazed at us, panting.

"Light," she hissed. "We will extinguish your Light, Traveler." Then she seemed to return to herself. She drew a deep breath and looked at the two of us, blinking her mismatched eyes. "Neko, where have you been? And who is this?"

"Kari," I whispered, tracing her with a futile healing beam. "This is the Traveler. It's come to heal you."

She gazed at the Traveler ghost, hope brightening her withered face. "Is it true?"

"Yes, my Guardian," the Traveler said in paternal tones. "Your ghost has agreed to hold your spark as I revert your body to its uncorrupted form. It will feel like you are dying. But you must remain calm. Trust me. Trust your ghost. Are you willing?"

"Yes, Traveler," Kari whispered, enraptured as if she beheld an angel. "Will it take long?"

"It will take a time," the Traveler replied. "But time is a fluid thing, with many whorls and eddies. If both of you endure to the end, you will live." It turned to me. "Are you ready?"

"Yes, Traveler," I said.

The Traveler ghost scanned Kari with its own beam of Light. It beam drew a glowing, golden shadow of Kari out of her body. Her body convulsed and went rigid, the eyes staring.

The Traveler guided the glowing shadow to me. I caught it in my own beam and drew it in.

Kari's spark entered my core with a cry. "Neko! Is this you?"

"Yes, Kari," I whispered. "Remember - stay calm. You're safe."

On the bed, Kari's corrupted body dissolved into red particles that swirled and vanished. The Traveler ghost vanished, too. I was alone with Kari's spark in my core.

She was warm and beautiful, burning alongside my own spark. "Your core is so big and bright," she observed. "I had no idea!"

"We're both made of Light," I told her. "Size has no meaning when you remove mass."

She laughed - her old, natural laugh, which I hadn't heard since her husband died. "This is a miracle, Neko, and you make it sound so scientific. How did you persuade the Traveler to help me?"

I squirmed a little. The embarrassment of the ghost trial still hung in my mind like smoke. "Well, I ... I asked. And it said ..." I trailed off. She was so near, there in my core. At this level, our sparks were the same shape, the same brightness. It's one thing for a tiny robot to tell a human that they love them. It's quite another to say such things soul to soul.

"What did it say?" Kari prompted. "Neko, you can tell me. There's no point in keeping secrets now."

She felt it, too - that closeness we shared. I looked anxiously at the empty bed, but there was no sign of her new body.

"It said," I replied delicately, "that it was willing to help because I loved you so much."

Her spark flickered, as if a shiver had passed through her. "Oh, Neko."

"You asked," I said. "And here you are."

"Here I am," she repeated, as if stunned. "I know ghosts love their guardians. We take it for granted. But ... Neko ... this is something grand. Is this why you're able to hold my spark like this?"

"Yes. The Traveler said that no other ghost has ever dared try."

Her spark flickered again, dimming a little. I lent her Light from my own. "Calm down. You're wasting energy. Don't burn out."

She flared up bright once more. "Neko, you're wonderful. I never knew how wonderful until this minute. I was always a little embarrassed when you'd cry over me, but I never thought ..."

"You're my Guardian," I said. "When you hurt, I hurt. When you triumph, I triumph. And I've failed you so awfully, Kari. I'm trying to make it right."

She laughed, then sobbed. Her spark dimmed again, her emotion consuming the fragile energy that held her together. I mended her with more of my own Light.

"You're not a failure, Neko. You keep saying that, but you're not."

"I allowed you to catch the infection," I said. "I forgot to have you treated once we came home."

"You were shot down," she retorted. "Then the City was captured. Those things weren't your fault. You went to the Traveler for me, Neko. It's building me a new body. That's an amazing success."

Her spark wavered alarmingly, like a candle flame in a breeze. I caught it and stabilized it with my own. But a sense of tiredness settled through me. Her spark was now brighter than mine.

"We're not through this yet," I said. "I don't know how long the Traveler will be gone. Hush now. We need to conserve our energy."

We sat there, silent, for some time. My spark began to brighten again.

"I'm the failure," Kari murmured.

"What?" I said. "No, you're not. You're a wonderful Guardian."

"I should have protected you on that Hive ship," she said. "Instead, I let you be hurt. Some Guardian I am. Then I didn't take care of myself when I caught that infection. I've had months to get it treated, Neko, and I didn't. Now here we are, and we're so fragile. We could die in a second."

Her spark flickered and dimmed. I gave her my own Light, dimming my spark still further.

"Neko," Kari said, her voice sharp and alarmed. "Stop doing that. You're going out."

"Calm down," I whispered. "The more energy you spend, the more I spend to keep you alive."

"Neko ..." Her voice broke. She shivered beside me, trying to control herself. "Don't kill yourself for me."

"I'm trying not to," I replied. "I can't leave you without a ghost. But I have to keep you alive."

We sat in silence for a long while. My spark remained dim. I would need days of rest to recover from this. I was tired in a way I never had been before, not even after hours of firefights with Taken.

"Neko," Kari whispered, "I love you."

My core warmed and a little Light returned to my spark. "I always hoped you did."

"I never knew," she murmured. "I never knew you were like this inside. I thought ghosts were just ... robots."

"We have souls," I replied. "I thought all guardians knew that."

"I never thought about it," she said. "I've seen dead ghosts before, but I never realized they were ... they were truly dead."

"It's why I got so upset whenever we found one," I said.

I heard the smile in her voice. "I thought you were just a softie."

"I am," I replied. "But only toward the people I care about. And you."

She made a whimpering sound, not quite a sob. Again, her spark guttered. I gave her my Light to keep her bright. My spark dimmed to the dull red of an ember in a dying fire.

"Neko!" Kari cried. "Don't do that! You're putting out your own spark!"

I could barely hold myself in the air. I landed on the edge of a bedside table instead. That's when I noticed a flicker of blue light across the bed in the shape of a human body.

"The Traveler's coming back with you," I said.

We watched in excitement as the Light resolved into Kari's former body, before the infection, there in the quarantine room. The Traveler ghost appeared with it, phasing through time, bringing with it Kari's body stage by stage. First the skeleton, then the organs, then the muscles and skin. Both arms intact. No hint of the awful thrall infection. I wanted to leap in the air and cheer, but I was too weary.

In a few minutes, Kari's body was complete. The Traveler turned to me. "Do you have her spark?"

"Yes, Traveler."

In the second before I activated my beam to transfer her spark, Kari touched me with her own. It was the lightest of touches, like a kiss on the forehead, but I felt her love. It made my own spark brighten a little.

I passed her spark out of my core and back to the Traveler. It took her and gently laid her soul back into her body, the spark settling into her chest.

Kari gasped and her eyes flew open. She sat up, moving her arms and legs, looking at her hands - both hands - and touching her face. "Thank you, Traveler," she said, bowing to its ghost. The Traveler acknowledged with a nod.

Kari lifted me off the table and held me in her cupped hands. "Neko, dear Neko, please don't die."

My spark was so weak. The energy she had given me had powered the beam to transfer her spark. My eye flickered in time with my own waning power.

"Kari," I whispered, "I'm so sorry. I'm about to fail you one last time."

"No!" Tears trickled down her cheeks. She clutched me to her heart. "Traveler, can't you help him?"

But the Traveler ghost had disappeared, its mission complete. We were alone.

She held me up and gazed into my eye, stroking my shell. "Stay with me, Neko. There's got to be a way to save you."

"So tired," I murmured. Inside me, my spark ebbed a little lower. I had passed the point of no return, having given too much of my strength to my beloved Guardian.

"No," she whispered, watching my eye dim. "Please, no."

"Don't worry," I said, barely able to force the words out. "The Traveler ... will take me home. With the other ghosts. I'll ask ... I'll ask it to send you a new ghost."

My core and shell seemed so heavy. How had I ever flown around? I was made of lead.

"I don't want a new ghost," she sobbed, pressing her cheek against my shell. "I want you, Neko. I saw your heart, and it's so beautiful."

"All ghosts are like that," I whispered. "No ghost could fail to love you, Kari. You're the best Guardian."

My spark wavered, on the verge of extinction.

"I love you," I whispered one more time.

Kari looked into my eye just as it went out. Her cry of anguish echoed through me as I spiraled away into oblivion. Beyond that waited the Darkness, hungry and waiting.

But as the Darkness reached for me, Light flashed from the other direction. It drew me in, protecting me from the evil that lurked beyond.

Suddenly I was back inside the Traveler, surrounded by living Light and other ghosts. They cheered and welcomed me into their midst. I laughed and cried at once, pure delight sweeping me.

The Traveler ghost was there, too. It embraced me with Light. "Welcome home, dear child. I'm sorry the price of healing your Guardian was so high."

"It was worth it," I said fervently. "Kari is healed and whole. I would do it again, if I had to. But ... please don't leave her alone. Please send her another ghost in my place. She's a soldier, and she'll die without one."

Here, in the Light, as pure spirit, it was easier to communicate. The Traveler's smile soothed and healed me, restoring the energy I had expended. "Love is as strong as death," it said. "It burns like a blazing fire, like a mighty flame. Many waters cannot quench love, nor can rivers sweep it away. Not even the Darkness can stand before it."

The Traveler turned to the vast assembly of ghosts who crowded around us. "What is your opinion, children? Should I send this ghost, this beloved Neko, back to his Guardian?"

We debated the question. This time, I was part of the argument, and I argued fiercely that I should return. "A Guardian without a ghost is one step above dead," I said. "If not me, then the Traveler should send another. But Kari shouldn't be left alone."

"That's against the rules!" other ghosts argued. "One ghost, one Guardian. They live and die together."

"But Neko's love is as strong as death," another ghost observed. "We all loved our guardians, but not like this."

"Yes! Exactly like this!" another ghost retorted. "Don't minimize our pain and loss! We watched our guardians die, or died in our turn. None of us were sent back."

"None of you ever came to me for help while alive, either," the Traveler observed dryly.

The assembly fell silent. The ghosts looked at one another, ashamed.

I faced the Traveler. "Are there rules? Am I breaking some law about being sent back?"

"Just because something is customary doesn't mean it's law," the Traveler said. "My law is mercy. I saw how you struggled to keep Kari's spark alive, my little light. You sacrificed yourself without hesitation. I know that, should you return, you will continue to do so. And so, my question to you is, do you want to return to the world of shadow and darkness, to weeping over your Guardian as she suffers at the hands of our enemies?"

In that lovely place, surrounded by my sibling ghosts, in the presence of the Traveler itself, I was at peace. I was safe. There was no Darkness here, no stain, no evil. My spark yearned to remain there, forever at rest.

And yet ... Kari was alone in that world of Darkness, without the smallest light to cheer and comfort her.

"Send me back, please," I said. "When I return to the Light in death, Kari and I will come together."

The Traveler smiled. In the warmth and power of that smile, the Light surrounded me, rebuilding my physical core, my base shell, every part and component forming out of pure Light and hardening into matter.

And then ... I was sent back.

I phased into being in Kari's tiny dorm room. She was asleep in her bunk, curled up as if in pain. But there was no black infection, no fever. Perhaps it was simply grief. I swept her with a healing scan. Yes, she had let her health sink below ninety percent. I restored her, rejoicing in my ability to do so.

Then I scanned her tablet to update my time settings. Two whole months had passed since my death. Two months! It had felt like minutes. My poor Guardian had been alone all that time.

My heart aching, I flew to her and landed on the pillow beside her face. "Kari," I whispered. "Kari, I'm home."

She opened her eyes and gazed at me without comprehension.

"Eyes up, Guardian," I told her.

She sat up with a jerk, eyes wide. I flew into the air and hovered in front of her.

"Who are you?" she breathed.

"Neko," I replied. "The Traveler sent me back. It was a huge debate. I know I'm wearing my basic shell, so I'm not very fancy, but - "

She snatched me out of the air and hugged me fiercely. "Neko," she sobbed. "It is you! I've dreamed about you so many times, I thought it was another dream. You're not another ghost with his memories?" She set me back in the air and studied my eye.

"No, it's really me," I said. "The other ghosts were furious that the Traveler would send me back and they never had that chance. But then ... I don't think any of them ever asked."

"It's been two months," Kari murmured. "I've been assigned to tower guard duty. Without a ghost, they can't risk me in the field. I've been dying by inches."

"I healed you as soon as I arrived," I said, glancing around. The usually immaculate room had clothes and armor tossed everywhere. "You've stopped caring for yourself? For shame, Kari. I'm not that important."

"You are to me." She grabbed me and kissed my eye, then polished away the resulting smear with her sleeve so I could see again.

I laughed. "Don't do that."

She stood up and reached for a hairbrush on the desk. "Now you're back to kick my butt, I'd better make myself presentable."

"Yes," I agreed, watching her with a satisfied possessiveness. "You're still my Guardian, and I'm going to take care of you until we both die and see the Traveler face to face."

Kari's lower lip trembled. "But not for a long time?"

"Not for a very long time," I said.

The end