As the group heads further in, you’ll hit an event flag. The three erstwhile semi-heroes are plodding steadily along in the knee-height water (which doubtless makes Sharla very glad of her thigh-high boots) when the medic pauses- and then says she hears something. Specifically, an Ether Rifle. Shouting Gadolt’s name, she charges deeper into the cave, emerging onto a small platform at the top of a ramp, in a room where Mechon are fighting someone who is hidden behind a metal box, firing back with an Ether Rifle. As Shulk and Reyn rush to catch up, Sharla opens fire on the Mechon, as the other rifle-wielder continues fending them off. Sharla calls Gadolt’s name again, but the reply comes “Medic, is that you?”
Realizing that this is Otharon and not Gadolt, Sharla darts down the ramp, running over towards him and blasting away at Mechon as she goes. Shulk sprints after her, telling Reyn to get a move on. With a cheer for the pending combat, Reyn follows on, the two of them jumping in front of the rifle-wielding Homs, ready to make some scrap metal.
This should be a very easy fight by this point- while there are four Mechon- a pair of M32X, an M43, and an M43X- all of them are level 20, and Sharla can actually do significant damage past their ordinarily impervious armor, even before Shulk uses the Monado Enchant Art. The biggest obstacle you’re going to face here is- well, the obstacle. The metal crate Otharon was hiding behind is part of the battlefield, and it can get in the way if you’re piloting Sharla and trying to keep out of melee range- or if you’re piloting Shulk or Reyn and have to chase a Mechon chasing Sharla around it in order to peel it away from your support character.
Despite this aggravation, though, the Mechon fall like particularly un-aerodynamic bricks without too much trouble, leaving your party with Otharon in the metal-floored cave.
As Sharla runs up to Otharon, he simply stands facing away from her, asking why she’s here. Ignoring the question, she asks Otharon how Gadolt is doing- but the gray-bearded man doesn’t actually give an answer, walking a few steps away and then declaring with melodramatic mystery that ‘there is much to discuss’. He then tells the party to follow him, and heads off.