Sorry Ôbout the cliffie! It was too perfect to pass up. Hiei and Kira meet again and, as Kurama predicted, there are plenty of sparks! The mysteries surrounding Hiei and Kira's shared past deepen.
Thank you, Ensatsu-Kokoryu-Ha, for all your encouragement.
I do not own any YYH characters. They belong to their author/creator Yoshihiro Togashi. The "Black Widow" name is also used by Marvel; I don't know anything about that character, so any similarities beyond name are completely coincidental.

Hiei regarded her impassively. "Draw your sword," he said in his deep voice.
"I don't have time for this!" Kira cried. "We can work this out later-- unh!" Hiei had struck her on the side of the head with the flat of his blade.
"We settle it now. Draw." Kira unsheathed her sword with enough force to push her opponent back. She tried to keep him back, to take advantage of her slightly longer reach.
Kurama and Kuwabara reached the corner, and were shocked to see Hiei attacking their new ally. Kurama yelled, "Stop! Hiei, she's a friend. Stop it!" Hiei mocked his opponent, "A friend? Who did you tell them you are?" He was much stronger physically, and the force of his blows were making her arms and hands go numb. Unable to continue blocking, Kira braced herself against the wall and concentrated on deflecting the blows just enough that they would go wide. Hiei was forced to stop using stabbing blows, for fear of snapping off the tip of the blade on the concrete. He said quietly, "You should have paid more attention to my lessons, Kira. You shouldn't put your back against a wall unless you are surrounded or injured." "I listened, sensei." Sweat stood out on Kira's face as she tried to match the speed of Hiei's strokes. Her sword-grip was getting weaker; she was using two hands now, but both were completely numb. She thought grimly, "Four more blows, and I'm finished. Not even a legendary sword can save me; I'm still too weak." "Hiei, stop!" Kurama yelled, as he stepped between the two combatants. Both froze, astonished. Kira slumped down to her knees, gasping for breath.
"KURAMA!" Hiei screamed, "What the HELL do you think you're doing? Do you really want me to run you through again?" Kira fully expected the anger in Hiei's voice, but was unprepared for the look in his eyes as he stared at Kurama: naked terror. His sword was trembling. When he spoke again, his voice was sadder, almost asking for forgiveness. "I almost killed you. What were you thinking?" "Like she said, we don't have time for this. Urameshi's in trouble." "Why do you trust that bitch? Do you even know what she is?" "I said before. She's a friend." Kurama crouched down beside Kira. "We have to find Yusuke." Kuwabara pointed out, "It looks like he found us." Yusuke sprinted around the corner a couple of blocks away. Behind him, the ground rippled. Thousands of the lizard-like monsters were chasing Urameshi; more waited in side-alleys, funneling the boy towards his companions. Yusuke fired his spirit gun; the vermin crawled over the ones who were charred by the blast and kept coming.
Kuwabara said, "Guys? I think we'd better run." "Hn," muttered Hiei, "For once, I agree with carrot-head." The main alley was blocked, so they raced down a side alley instead. Kurama asked quietly, "Does it seem like we're being driven someplace in particular?" "Doubtless where Takho's waiting with another thousand of the demons," said Kira.
Kuwabara stopped. "Then we should make our stand right here." "No good," Kira panted, "the only way to stop the vermin is to kill Takho. At least he's leading us towards him." Hiei rounded the corner and skidded to a stop; Kuwabara tripped over him into Yusuke, who shoved Kurama. There was a wall of monsters slithering over each other directly ahead. Before they could start yelling at each other, Kira called, "Listen up. Takho's a shape shifter, so we can't trust any lone individual, got it? He can assume the shape of anyone important to you, so if you see any of your dead girlfriends, kill her again. Hesitate and he'll kill you with a poisoned needle." She kicked open a window leading to the basement and called to the others, "One of you should come with me." Kurama stepped forward, but Hiei pulled him back. "There's no way I'm taking my eyes off that bitch." Kira said, "Fine. Hiei's with me. The rest of you, search the basement of the building opposite us. Kill anyone who shows up without his partner." Yusuke interrupted, "Why are we searching the basements?" "The assassin likes his rat-holes dark and cramped." She disappeared through the window. There were the sounds of a sword slicing through meat, then she called up, "Hiei, I could use some light." Hiei jumped in after her with his hands ablaze. The air became thick with the smoke and stench of charred lizards. The mortal flame lit the room almost as well as electric lights. Kira kicked open one of the closet doors, then moved to the next. There was movement inside the second closet. Hiei saw a glimpse of light blue hair and red eyes from a demon no larger than a child. Kira's sword slashed out, but never connected; an unexpected blow from the side knocked her off her feet. Hiei had struck her with the dull edge of his katana and stood protectively in front of Yukina.
"Baka," Kira hissed.
Hiei snarled, "I won't let you hurt Yukina!" A throwing knife whistled through the air past Hiei's right ear and buried itself in Yukina's wrist. Four long needles plinked to the concrete floor. Yukina wailed in pain and screamed, "You bitch! I'll gouge your eyes out!" Then she turned her great red eyes on Hiei. "Won't you please protect me?" she pleaded.
Hiei backed away from her, horrified. Kira said, "Kill her, damn it!" Hiei could only shake his head and back away. "If you can't kill her," said Kira, "then stay out of my way this time." Yukina turned her huge eyes on Kira as her elfin features melted and reformed themselves into those of a four- or five-year-old boy. He cringed before the demons and begged, "Don't hurt me!" "Kuso," Kira whispered as her sword hissed through the air, "You're a real bastard, Takho." There was the unmistakable sound of a sword slicing through flesh and bone, then the head rolled off as the child's body fell.
Hiei watched the lizard's bodies shimmer and fade away into nothingness. He then looked up at Kira, who was calmly wiping her sword on the child's corpse. "Why doesn't the demon assume it's true form? Now that it's magic is gone . . ." Kira shrugged. "I'm not positive this rat had a true form. You'd better put out the flames; there's not enough ventilation in here to prevent suffocation if you use up the oxygen." Hiei extinguished the fire with a wave of his hand; only a single magical flame glittered in his left hand. "Who was the kid?" "Dunno," said Kira, "Just an attempt to appeal to my maternal instincts." Hiei could tell she was lying by the casualness of her voice. "Was he a brother? Or . . . Kira, did you have a son?" The flame picked out highlights in her short, spiky hair as she turned around very slowly. Her eyes glittered within dark sockets. They stood for several long moments, looking at each other.
When Kira spoke, her voice was husky with suppressed emotion. "A child? Me?" Her derisive laughter cracked. "Me bear a child into this hellish world? I'd be even more of a bastard than you." Hiei grabbed her arm. "You would have preferred that I left you to bleed to death when we first met?" Kira looked down into the ruby eyes and sighed. "I know you did all you could for me. But when you went away, you left me with nothing but the blood on my hands. Letting me bleed to death years ago would have been a mercy." The flame Hiei held in his hand was reflected in the young woman's eyes. Yusuke and Kuwabara's loud voices came from outside. Hiei vaulted through the open window to join them. Kira pulled herself up part way with her arms, then felt strong hands tugging her the rest of the way through. She didn't meet Hiei's eyes as he helped her stand, and he didn't try to meet hers. The wounds from seven years previous were still unhealed.