This show is disgusting, unfunny, incoherent. And yet... it's a favorite of mine. I don't remember how often I've rewatched it over the years. It's the same thing every time: I wonder what's so special about it, press play, fall in love with the artstyle. Smooth, fragile, soothing. I frown over the distasteful sexual jokes. Some are funny, but most of them focus on kids. Don't know about that. I listen closely to Naoko-san's voice. Her manner of speech is weird, but to me, somehow very nice to listen to. I shake my head at the weird turns of the story. Supposedly funny because it's random? Meh. I realize thatover two thirds of the OVA have passed. Seems I've seen something in it that wasn't there.
I feel the disappointment creeping in. But there is something else.

Gentle artstyle contrasting with violent actions.
Innocence of children contrasting with harsh sexual jokes.
Family contrasting with alien lifeforms.
Beneath all of this, the feeling of loss and helplessness. What happened to Misuzu's sister, why was she "replaced", why by someone who is nothing like her? All this time Misuzu is getting dragged along, quietly accepting her fate. What is Naoko-san trying to achieve, why is she so focused on Misuzu, is she trying to distract or console her? Is she her sister after all?
The ending song hits. Misuzu feels like she was abandoned by her sister, yet she wants to go to such a forsaken place. Because she feels understood there? The imagery goes very well with the song, and at this point, I'm completely sold.

To me, it's a show of extremes accompanied by a sense of strange longing, creating a feeling I haven't experienced anywhere else.
I can't say whether any of this was deliberate, maybe I just like the ending song and read way too much into it, but to me, it doesn't really matter.