Isn't there a line she has like "Iku no" or something that is similar to "I'm coming?" Or am I missing the joke completely?
From what I understand, Imuya probably stuck the lava lamp inside Iku, because of what she said(I suppose Imuya didn't want to admit she's happy or something), so there's no joke on the "Iku no" quote. But when Iku said Imuya was happy, if I'm not wrong she finished her sentence with "-no ne"("ureshii no ne", if I'm not mistaken), which Iku says quite often, at least compared to the other subs, thus identifying the legs as hers?
Ihihi...This place will be your house from now on.I... I'm coming!Will you remember it?You must be happy to have a kouhai now aren't you, Imuya?