I'm looking for a novel to read with a really big harem (20+) like Ancient Strengthening Technique, Womanizing Mage, and My Beautiful Teacher.
I don't know anything about the series you say you like, but these all have large harems of 20+ and in a couple of them the MC manages to get his harem members pregnant too. Oukoku e Tsuzuku Michi Kujibiki Tokushou: Musou Hāremu ken Charging Magic With a Smile Isekai Nonbiri Nouka
30?! It'll be a headache remembering just their names, let alone their birthdays, anniversaries and stuff! XD
You can try this; https://www.webnovel.com/book/13282409505305605/Profane-Prince-of-Domination If I remember correctly the harem goes into the 1000s, though this is more like porn with plot.
Tbh, that one is quite good at the start, but I got told that it had NTR towards the later part and ending was shit. That made me drop it halfway...
Yeah, I dropped it after I got told these. Essentially yeah. The plot itself is quite intriguing, but majority of it is just porn, same as with most of the massive harem novels.