That is a super specific fetish.

bunkhead said:

That is a super specific fetish.

I think in this case it's referring to Senko.

Senko doesn't really seem like imouto material. Too much of an old soul.

CharleyDodger said:

Senko doesn't really seem like imouto material. Too much of an old soul.

Imouto on the outside, onee-san on the inside.

UserAccount said:

Imouto on the outside, onee-san on the inside.

That's not how it works, if it ain't quacking like a duck it ain't a duck.

bunkhead said:

That's not how it works, if it ain't quacking like a duck it ain't a duck.

I think his point was that she looks imouto but acts oneesan.

UserAccount said:

Imouto on the outside, onee-san on the inside.

More like an okaasan (bordering on the obaasan, if you consider her receiving a massage) on the inside.
...and the imouto part? More like the shortstack oneechan type (Shiro fits the imouto part better.)