Tortoise in Time

“

Bunchin has not heard from Soroban in quite some time...

— In-game description

Rewards

To enter Reisen Temple, talk to the tanuki named Furi at (x:27.1, y:38.3, z:0.1) in The Ruby Sea.

After talking with Genbu, a solo duty will commence. In this fight, Genbu and Tataru will join you against Soroban from the start.

Soroban uses a lot of AOE attacks, so you have to keep moving.
When half of Soroban's health is depleted, Genbu will instruct you to get behind him as he erects a shield. Afterwards, he will retreat from the battle.
When Soroban is near defeat, he will summon up Fonts, which are basically large whirlpools. Defeating these aren't important, but it does help make the fight much easier.

When last you left Soroban, he was undergoing strenuous training under the tutelage of Genbu, one of the Four Lords of legend, in Reisen Temple. It would seem that since you delivered news of this development to Bunchin, he has heard nothing further regarding his kinsman. Coincidentally, the moment the Kojin chieftain voices his concern, you are contacted by Tataru, who is bound for the temple to deliver a treat to the hardworking Soroban...

Though Soroban is not without potential -- as is evidenced by the simple fact that he has yet to run screaming from the temple -- Genbu is concerned that he will not be strong enough to aid in the great battles to come against Seiryu and Suzaku. Therefore, to accelerate the training process, he would have you retrieve a relic known as the tamate-bako of geomancy, which has the power to manipulate time itself, and transform Soroban into an auspice -- albeit until the magicks dissipate. The box can be found deep within the Swallow's Compass, the ancient mausoleum of Ganen, the founder of the Kingdom of Doma and father of Far Eastern geomancy. Given the nature of the task, it would be prudent to call upon several of your allies.

You journey unto Yanxia and arrive at the tomb to find Kamaitachi, who has already dealt with the wards sealing the entrance. The grand mausoleum was long ago abandoned to the shikigami forever bound to its halls, who will doubtless do their utmost to bar your way. Nevertheless, you and your comrades must overcome these guardians and whatever other trials you encounter, and lay claim to the tamate-bako of geomancy.
※The Swallow's Compass can be accessed via the Duty Finder.

After braving the myriad dangers of the tomb, your party at last comes upon the relic and its final guardian, an auspice far more formidable than those who preceded him. Yet, in the end, he and his golden-hooped rod are no match for you and yours.

Genbu is quite pleased to receive you and the tamate-bako of geomancy, and immediately calls for everyone to prepare for the next stage of Soroban's training, in which the Kojin is to bathe in the temporal magicks of the box and temporarily transform into an auspice. The process is not without its risks, however, and despite Tataru's assurances that she can bring her arcanima to bear in an emergency, it will likely fall to you to deal with any dangers that may arise...
After all save Soroban withdraw to a safe distance, the Kojin opens the box, from which pours forth an endless fount of smoke. All observe in silence... until Tataru, growing impatient, declares the box to be a fake and runs to gaze inside. Genbu quickly pushes her aside, but too late to spare her entirely, as she is transformed into a hideous crone... for some few moments. Alas, her reckless actions serve to distract Genbu from Soroban, whose prolonged exposure to the smoke leads him to transform into an auspice already consumed by the aramitama. As feared, you will need to call upon your martial prowess and subdue the rampaging Soroban before Reisen Temple is destroyed.

Though the battle is not without its twists and turns, it ends in your victory, as is usually the case. Genbu, briefly incapacitated, has fortunately recovered, and regards Soroban with a mixture of surprise and exasperation...