It wasn’t often Kakuzu got injured, but Hidan had seen it happen while they were in the middle of a battle and it seemed Kakuzu either hadn’t noticed, or it wasn’t enough to bother him.
As soon as he could, however, Hidan was lifting Kakuzu’s cloak out of the way, looking him over all while Kakuzu protested, until he found it: a gash above Kakuzu’s hip and towards his back, still bleeding.
Hidan patched him up as best he could, fighting off threads that could have done the work for him, but sometimes Hidan liked to take care of Kakuzu, even if he wasn’t that good at it and the bandages fell off somewhere between then and the next town.