It's good that Kisame is so understanding, Itachi thinks. The shark is always willing to stop so Itachi can relieve his aching bladder, never mentions the sheets in the washer or the plastic cover on the younger Akatsuki members mattress, and doesn't tell anyone about the boys (many) accidents on missions. Once, Itachi slept in Kisame's bed because he was injured, and woke up to find that he'd soiled himself and his partners sheets, but Kisame was surprisingly gentle about it. He sent Itachi to take a shower, changed the sheets, flipped the mattress, and they never spoke of it again. After that, however, Itachi bought a package of adult diapers to wear at night. He still refused to wear protection during the day, saying that his accidents are so infrequent he didn't need them. This isn't exactly true-the teen wets almost every day, and he can barely hold it for an hour. His illness has severely weakened his bladder, and he has trouble controlling it at all. Although he doesn't show it, Itachi likes allowing Kisame to care for him, but only a little. The shark often asks if he needs the toilet, or tells him to use the restroom when he feels that Itachi's waited too long. Sometimes he reminds the boy to go before bed.
Once, when Itachi was bedridden, he threw up on himself. The Uchiha stared down at the mess he'd made, then called out for Kisame. His partner was so kind about it, helping him into the bathroom and washing him off, then softly asking if he needed a change. Itachi looked at the wall and nodded shamefully. Kisame changed him quickly, then took him into his room and tucked him under the covers while he changed the boys sheets. They never talk about these incidents, nor do they mention the nights when Itachi runs into Kisame's room with tears streaming down his face, sobbing that he's sorry, whimpering his little brother's name. He throws himself into the sharks arms, trembling, and Kisame holds him until he calms down. No, they don't talk about these things, but they both acknowledge them, and they both know that they've fallen into a sort of father-son relationship. And of course they'll never tell each other, but Itachi likes being treated like a child, and Kisame likes treating him like a child. It's a strange little arrangement, but they don't mind.