Really? I've been getting more of a sibling vibe than a daughter one.
Still, Big brother instinct is also a thing.
Nah, think about it. Senketsu has been very overprotective of Ryuuko for the entire series. Seeing how this series left bombshells left, and right. Also Ryuuko's father, faked his own death, and might have been turned into a life fiber cloth, Senketsu being Ryuuko's long lost father would make a TON of sense.