Checking the raws of volume 3 it seems like the Mangaka uses the ecchi aspect like someone dangling keys to get attention from impressionable toddlers, is quite random, doesn't seem to add much, is another case of "overly expansive gal goes to MC's house, randomly sleeping half naked around him while he has a panic attack........and he is supposed to be an adult.
Checking the author's other work I found he wrote sundome, something I dropped in rather early as it was quite boring. Maybe I'll read it once is fully finished and IF I know it goes somewhere or is just another case where it could have been a slice of life but the author tackled in a girl to fool readers.