The Resurrection Hot Springs!!

Summary
Mirai initially declines Tatsumi's invitation to meet with the dead, but later changes her mind upon reflecting about all the comparisons people have made between her and her father. They head out in the night, as that's supposedly the only time the dead can appear. Mirai rationalizes this trip by insisting to herself that they'll return by morning, before Kakashi and Guy even realize she's gone. She also feels that Tatsumi needs her: the journey into the mountains begins to tire her and she asks if they can replenish their water bottles at a nearby hotspring. On tasting the water, Mirai finds it unpleasant, but Tatsumi remarks that its metallic content is supposed to have restorative properties.

They arrive at their destination, a deep cave behind a waterfall. A ritual is already underway, with several young girls waiting nearby. Mirai becomes suspicious, but Tatsumi happily greets the leader, Ryūki, who she says can give special powers to the local hotspring. Ryūki is friendly toward them both and offers Mirai a drink to officially induct her into their group. Mirai pours out the drink, assuming it's drugged. Ryūki ceases to be friendly and has Mirai restrained. He reprimands Tatsumi for bringing somebody so perceptive, but insists the ritual will continue regardless. To his surprise, Mirai quickly fights off his followers and asks for more information about the ritual.