The bare outline of the plot makes sense, but the execution is lacking. It's all rather too much explain-the-plot dialogue, spread out with random mofu moments, and no time at all was spent to make the main character likeable or interesting. It needed to take the time to breathe, chill, and grow the characters and their relationship.
We get why he fell for her -- given the titular mofu onee-san, the kid didn't stance a chance -- but aside from a throwaway childhood scene, we don't get why she cares, and it make this feels like an empty wish-fulfillment piece. Here's your magical blanket girlfriend, go hug her a lot, 'k.