The Fifth Hokage gambled on a forbidden jutsu. The jutsu won.
Tsunade has faced down war, debt collectors, and the worst luck at any gambling table in the Five Nations. What she hasn't faced is her own chakra turning against her. Cracking open a sealed scroll she was warned to leave alone, the Slug Sannin triggers an experimental regeneration jutsu that does a great deal more than enhance her strength.
What starts as a routine power-up spirals fast. The transformation surges past anything in the scroll's notes, leaving Tsunade gripping her desk as her legendary control slips and her body refuses to stop changing. Shizune can only watch, helpless, as the most powerful kunoichi in Konoha discovers exactly why this jutsu was sealed away.