Far as I read there are at least two confirmed harem members (though not sure if the MC knows it yet) as far as I've read. First is called Mina and is introduced really early on, however in the novel no real description of how she looks is actually given when she's introduced except that she's a mage while in the manga she is shown as a dark haired big oppai girl. The 2nd girl introduced but kind of the first harem members since her mom basically pushes her onto the MC is in the novel (though again unsure if the MC even understands since he's so dense) only given the description she's a blonde haired girl named Lilliera that the MC calls beautiful upon their first meeting, pretty sure that she is the blonde big oppai girl shown on the manga cover.

So from what I saw the MC is only in permanent party with Liliera. there might be other girls around MC but they are temporary and just friends or apprentice lol

And most importantly, Mina that the other reviewer mentioned, is not one of MC's "harem" since its pretty clear the author ship her with Jairo, they always bicker around and beat each other and people even joke about they "flirting" and such.

in fact, most of the girls are in Jairo's Dragon Slayer's team and while they get training from MC from time to time, the only one always traveling with MC and in MC's team is Liliera.

Overall the MC is dense so you simply don't expect any romance, but so far only Liliera is actively into MC and her mother also cheer her on about it or people in the story tease the MC and Liliera about being a couple or flirting.

There is like ~15 volume worth of Web novel out there so I don't know if there is other girls eventually, but Mina is not one of them xD I peeked the raw in some ~250+ chapter and Mina and Jairo are still being teased as a couple and not the MC.

in Fact, out of 8 LN Volume Cover, 6 of it is MC & Lilirea, 1 of them is MC and another girl important for an Arc, the other one is Mina & Jairo together and no MC.