Sango's heart seemed to stop as she recognized the youkai's intended victim: Kohaku. Her brother was here. And he was fighting for his life. Instantly, and despite any denial she might have made to her friends, her instincts as his sister and a fellow slayer kicked in.
Even if he was still under Naraku's power, there was no way she could simply stand by and let him be killed. Not when he was the only one left. Not when he was still her brother and there was a chance, however slim, that he might yet be saved. She urged Kirara to move faster, but they were still too far away to help effectively.
The beast's tongue shot out of its mouth, like a frog's, only fast and powerful enough to cause serious damage on impact. Kohaku dodged the first strike, but the youkai was not deterred.
"I think it's after his jewel shard!" Kagome shouted.
"It's what?" Sango's mind raced. Kohaku's life depended on that shard. Without it, he would die. She could not wait another moment.
This beast was no serious challenge for a trained slayer; the hiraikotsu slashed through its forelimbs and face, leaving it a crumbling mess after only a single strike. Sango leaped from Kirara's back to catch her weapon on the return, then strode quickly toward where her brother was waiting.
He was bleeding from a wound to his upper arm, but otherwise he looked exactly the same as the last time she had seen him. The last of her kin to survive, however tenuously, it filled her with relief to see him again even as she knew she must be wary. He was under Naraku's control, or at least he had been before. As such, he would likely have been at the castle… so why had he been left behind when it disappeared?
When Kohaku turned to face his rescuer, he frowned slightly. "Do I know you?" he asked, and it broke his sister's heart.
For just a moment, there had been a flicker of recognition in his eyes… and then it was gone.
Sango told herself to be careful, to not make the same mistakes all over again, to remember that this boy was not Kohaku, not really, but in the end her heart won out. He was her brother. She couldn't leave him here even though she knew this must be a trap. "Come with us," she said. "We'll protect you."
He glanced nervously between her—armed and armored and accompanied by a fearsome youkai of her own—and the remains of the beast that had so recently tried to kill him. After that, it seemed, there was no question for Kohaku. He ducked his head and agreed to come with them.