Because she's full of jealousy.
She can't enjoy Yuuta being happy.
Because Utah is a smart man and knows she will be less retared in a few years and have her sister body
No, please elaborate.
Do you think that docking with Deko would calm her down? I mean, there really isn't much there.
Rikka showing interest in marine biology was the last good thing to happen in the show. SoL is good and all, but come on, develop things a little.