(Note: This will be more of a rant than a proper review.)
Given the art quality of the cover and the synopsis for this novel, it made me a bit interested to see how the story for this one would turn out. Considering that I am currently reading works like Tensei Shitara Slime and Konjiki no Moji Tsukai and is waiting for new releases. But at this point, 2 volumes in and I have say that I would have to give it a drop for this one.
More than 10 chapters in, I have yet to see any real progress of even a point to this story already. Granted, that other than the protagonist we have complete newbies from Japan who were summoned to the Demon Capital, the protagonist has spent this entire time doing relatively nothing other than fixing the Demon's Castle. I would have stuck with it more if the characters and their interactions were remotely interesting, but as of yet the reader is introduced to little girls, and for some reason they all hug the protagonist at first sight even if some were complete strangers. I've read and came across Princesses who were ignorant (e.g. Altina from Altina the Sword Princess), but never have I seen before girls that were completely whiny and useless upon first impression (demonstrated no real useful skill or ability as of yet). But I guess that's harem for you.
Story: Is rather on the slow side, where even though I only read the Demon Lord summoning phase, there was no real mention of the world and politics. Even yet, no comprehensive mention of the world's power system
Characters: Didn't leave a good impression honestly. Protagonist sure liked to spend his time leisurely in the castle despite wanting to save his first love, Onodera and his otaku nature creeps me out, the Elf Princess being in loli-form creeped my out by saying...
Spoiler
"Let's make babies!!! :D"
... the first time she was introduced, the other maid girl who (granted) was taught "things", and then there is the idiot Sucubuss Princess who for some reason is physically or magically weak all the time.
Conclusion: Would I recommend this? Personally no, since I am the sort of reader who needs a "point" or real progression to a story at least a few chapters in. Other than the initial twist of the protagonist being summoned to the Demon's side as supposed to the Human's, there is nothing remotely interesting to note in regards to story progression or characters. I would recommend works like Sendai Yuusha wa Inkyou Shitai, who also presents a similar story of a former hero who went on a time-skip, or Konjiki no Moji Tsukai where the protagonist has taken survival matters into his own hands.
... But hey, if you're the type of person who has the patience to go through a slow progression story and cringy characters, then by all means I am not stopping you.