Well, from what Tonbokiri has told him so far, Ichigo has the impression that Sengo is the troublesome younger brother actually...

Ichigo laughs a little at that as he continues squeezing and wriggling his way into the dense foliage. "I suppose that's true, though the troops are significantly smaller!"

Then after a little pause. "Are you sure they went this way, Sengo-dono?" Because he's not seeing any trace of them...