Edit 4: The lawful-good use of this scheme is to tell all of that to Asuma and suggest sending us on a diplomatic mission to Mist/Sand/%insert minor village%. He could give us special dispensation to make binding agreements on Leaf's behalf, and we could use it to dupe everyone and funnel all their secrets to Leaf. This sounds like an immensely interesting arc, too. (Or, we don't even have to tell Asuma about TLitF, just claim we have a clan-secret way to do that.)
Duping someone into sharing information in exchange for some commitment, then erasing their memory of that entire meeting (could even be used on people we don't want to alienate, e. g. Leaf ninja!).
Damn, now I want to encourage Mari to embark on an extended campaign in which we steal the secrets of everyone in Leaf. It's basically a perfect crime. Invite a ninja for a meeting, covertly cast TLitF. Propose clan secret exchange, invent some reason why the trade needs to happen
now. Hand our secret over first to demonstrate goodwill. As long as they don't know about TLitF there'd be no reason to suspect foul play, so they should agree. Once we have the secret, erase their memory of the exchange and go on to strike some more boring business deal as cover.
As long as we're not targeting someone who can no-sell Mari's genjutsu with sheer CR, we'd be unstoppable. If the mark notices Mari casting TLitF, we just activate it immediately, dumping their short-term memory, their seeing the jutsu cast included. If they somehow notice the genjutsu (how? we wouldn't be exactly moving around, all Mari needs to do is get a static room with three people in it right), and try to break out, activate it immediately. If they don't agree to conduct the exchange, wipe them and start over. The whole thing shouldn't take more than 20 minutes and medieval clocks aren't very precise, so they shouldn't notice the time discrepancy and we could engage them in activities in which they'd naturally lose track of time afterwards to further mitigate it. TLitF is pretty unbelievable on priors anyway, so external observers somehow figuring everything out from random circumstantial evidence seems implausible.
It's bulletproof!
Except we wouldn't be able to publicly
use any of that stuff afterwards, bah. Unless we invent some bullshit "we found this in Jiraiya's stash/a Summon gave it all to us out of nowhere, we didn't know those were your clan secrets, wow awkward!" excuse, but
that seems flimsy.
Edit: We still could use it to get blackmail on everyone, though! Let's do it.
Edit 2: Oh, and we can certainly relieve Sasuke of all his
foreign ninjutsu, since we could plausibly have stolen it from elsewhere.
Edit 3: And the secret seals of all of those sealmasters! Those we can certainly plausibly claim came from Jiraiya's stash, and if instead of using them directly we tweak them slightly so the object-level effect is unrecognizable, no-one will know at all.
