Kouguu no Omega has two parts / volumes
Vol. 1 is ch 1-6
Vol 2. Is ch 7-12
"Vol 3" is actually the sequel called Omega of the
Harem: Snow Flower Chapter
后宮のオメガ 雪花の章
Spanish vers until volume 3
https://zonatmo.com/library/manga/62878/kouguunoomega
https://es.novelcool.com/novel/Kouguu-No-Omega.html
https://dragontranslation.net/manga/kouguu-no-omega
officials:
https://www.mangago.me/read-manga/palace_of_the_omega_official/
Kouguu no Omega