, no actaully she was the 1st person older than Tsunade who had it. I wonder how can you guys forget that and bash on the newbie. Hey you guys stop being harsh on the rookie, lets be nice to each other okay? Now You know that is a great question from someone like him. For starters the Byagoku seal was not developed by Tsunade, but instead Uzumaki Mito developed it, no actaully she was the 1st person older than Tsunade who had it. I wonder how can you guys forget that and bash on the newbie.
Personally I think Katsuyu was never meant to be a summon to heal people, but Katsyus speacility is the ability to amplify or tranfer the medical chakra her summoner gives her. This.... its simply because Tsunade used Katsyuyu as a medium to heal people even if she is away from the people she is treating. Its like katsuyu is tsunade's hands that can help her heal many people at once instead of her healing people one by one. So to answer your question I dont believe byakogu seal is a sage mode from shikotsu forest its a sealing jutsu. As the name says.. yeah someone said this....You must be registered for see images