Reconfirming that nameless adventures can't be sacrificed for the NIN trial per anon's observation earlier, I geared up a dwarf-kni just for this (unnecessary to actually gear them up, just swap your MC to Knight if you have that leveled and put your sacrifice in the back, there's a fountain near the end so you can go all out with heavy striking your way asap to end fights).

after the final confirmation, the dude just tells you to go back home because your "bond is too powerful", which I presumably isn't intended since nameless adventurers have no bonds to begin with. Also as a bonus, you're left with a dead body and having to foot the bill on reviving them