Restrict: koto, 7th-8th gate.
sc2: Gai starts in 8th gate, can danzo outlast gai? 100ft distance.
Dope ass sig dude.
Scenario with unrestricted Gai is an obvious win. I think with the restrictions of going no higher than 6G's is an interesting fight, but I'll side with Gai. Any stamina and gates repercussion concerns was tossed out the window in the war arc, when Gai was going in and out of his gates mode for long durations without any issue. The man can literally muster enough energy to go into the 7th gate and use Hirudora while already being at his limit... The 6th gate takes away far less body stress and energy, so being able to utilize it at will for 10 minutes (or however long it is) is legit not even a slight issue.
If Gai just keeps moving around, Izanagi surprise spawns will never work. Alternatively, summoning his tortoise to cover his backside to conserve energy is viable. With his reaction, movement, and striking speed, Danzo get's pummeled in every single CQC engagement until his time limit ends. Baku is never an issue as Morning Peacock hard counters, and with Gai's speed, he could likely maneuver around it's backside before the suction even takes place.
After a hard fought battle, I can see Gai taking it with high diff. I'm also assuming he has intel.