Sanzo coughed up blood one day, and then they were attacked by youkai. Not the other way around, as would be expected if he were injured in a fight. They were driving, and he doubled over, and they were attacked. Hakkai vaguely recalls Goku leaping to balance precariously over Sanzo, fiercely protecting him from the descending claws. He had, himself, been frantically searching through his mind for possible reasons. Old wounds, bad food, illness, smoking - almost anything. His hands had automatically begun to gather his energy, but he halted abruptly as he realized he'd need it to heal Sanzo. If he could. Shit. Soft tissue damage, almost certainly, but what if-
Claws sank into his shoulder, and he choked on a startled scream. Gojyo's shakujou whirred by his head, making him freeze to avoid decapitation, and he heard a wet crunch. Remembering the battle, he spun and elbowed the corpse aside and flipped the next attacker neatly over his shoulder. From then his body was on autopilot, disabling his opponents without really thinking about it. He caught glimpses of the others through the flow of the fight, and Sanzo seemed to have recovered - his first thought was relief, that Sanzo might be alright, but then he saw the tight muscles under Sanzo's eyes and he knew they would have to hold him down to care for him.
Rather suddenly, there were no more attackers, and Hakkai stalked over to Sanzo before he could escape and, putting a hand in the center of Sanzo's chest, he calmly pinned Sanzo against a tree. The too-tight muscles under Sanzo's eyes twitched, and that was his warning before Sanzo would forcibly push him aside, he knew, so he pinned Sanzo's hands as well.
"Shit, Hakkai-" Gojyo's hand on his shoulder was gently warning him, but he flicked a look over his shoulder and the other man fell silent.
"Let go." Sanzo tugged at the firm grip on his wrists, and Hakkai thought regretfully that the tree bark must be leaving imprints. He simply smiled and worked to get a hand free without releasing Sanzo's wrists, pressing it against the priest's chest the moment he could. It was never easy with internal wounds, but he's tended Sanzo before, closed wounds deep enough that he could see Sanzo's lungs flutter wetly. The feel of his energy pulsing through Sanzo's organs was not a new one, but nonetheless it was difficult to feel the difference that should signify the damage within him. It dawned on him that this is because the damage had been too gradual, that he had thought it to be the natural, unique feel of Sanzo's lungs, irritated by smoke and injury and a million other hardships. He cursed himself silently and tried to compare them to Gojyo's lungs, which were hopefully in better shape, but were the only other smoker's lungs he was familiar with.
"What's wrong with him?" Goku's tentative question nearly snapped him out of his trance, but he focused once more and didn't answer. No one answered, except that Sanzo muttered a curse. Slowly, Hakkai let go of Sanzo's wrists, but he didn't realize he was falling until Gojyo caught him. There was anger in Sanzo's eyes as he rubbed roughly at the red imprints on his wrists, but Hakkai knew better than to think it was directed anywhere but inward. He did, however, startle when Goku reached for Sanzo's hands and gently brushed his lips against the marks. Goku didn't meet anyone's eyes, didn't say anything, and Sanzo pretended it didn't happen.
"You're… You've known for a while, haven't you?" Goku asked, but he already knew the answer. He was trembling slightly, and Hakkai looked away, saw Gojyo look away as well, so none of them were watching when Sanzo rested a hand on Goku's head. Gojyo coughed incriminatingly, though, and it would be funny if it weren't so serious.
"It's not important," Sanzo murmured, and then he walked away. Hakkai wanted to laugh. He could feel Gojyo's anger behind him, and that struck him as hilarious, and Goku's dead eyes were the funniest thing of all. His shoulders were shaking, holding it back, and when Gojyo wrapped an arm around him he wanted to turn and tell him that these aren't tears, don't you see the joke here? But he's wise enough to hold that back as well, and instead he covered his face with a hand and tried to ignore the wetness he felt there.
Sanzo paused and looked back at them. "Well?" he demanded. "I'm not going to wait forever."
So they gathered themselves together and followed.