Depending on intent, that might still not exclude her viewing him as a little brother. (Sisterly affection and all that.) She's definitely shown signs of missing the "big sister" appellation.
Hah, if you ask certain people, being siblings just makes it even better! >:)
Ask Murakumo herself.You bring that up now?Atago and Maya, you two were sisters!?
Resemble
There isn't much resemblance, is there?Do sisters resemble each other? Brothers too?So you foisted it off on me.Well, in general, yeah.So someday I'm gonna become like Murakumo?