Izō is here because someone (a ghost of Ryouma) has also led him astray. His pants are soaked through well above his knees, which suggests how far he'd managed to wade out before he'd been stopped. Lucky.

It seems he has no choice but to pay that luck forward though because he feels drawn to another presence in the gloom.

"Oi! Snap out of it!"

Helpfully, Izō has been carrying a sturdy branch with him — it helps him feel less unarmed — and so he has that in hand to use as well. If his grating voice doesn't wake Siegfried up, the bonk might, at least..