
There you’re wrong.
In the latest chapter both parties confirm that they want to stay together forever and that they love each other, they kiss each other and goes back home holding hands. Then this doesn’t look like it’s going to be an harem because he’s definitely in love with elf and elf loves him.

Hi, thanks for your reply! I don't believe I mentioned a harem and only mentioned a "one-sided love atm." But, if you wish to discuss technicalities, that's all right.
It is possible to still have a harem in this case. I'm using harem in the manga/anime definition and not the one about concubines or mistresses. The protag. can still be surrounded by people who harbor feelings for him or her. He could possibly still be the subject of interest to a myriad of people even if he's only involved with one person on his side. My warnings still stand, as I only mention my thoughts on the elf girl and what it looks like to me.
Hmm, anyways, if you like this, go for it. If this isn't your type of manga, it's okay too. (▰˘◡˘▰)
It was very promising start with the interesting elements that everyone likes such as reincarnation, gaming world, OP character. But then, there's also ecchi and forced (one-sided atm?) romance to appeal to the very general readers who starve for romance subplot. :) The elf girl is literally like any other side female characters in those adventure mangas featuring a male protag. I'm not saying this is a bad manga, but it's very cliche. Just beware!