Happy no Hiketsu (ハッピーの秘訣)

I Was Reincarnated as the 7th Prince so I Can Take My Time Perfecting My Magical Ability

In his past life, Prince Lloyd de Saloum was a commoner who could not become adept at magic, no matter how knowledgeable or obsessed he was about it. Now reincarnated into his current royal lineage, he receives a body with seemingly endless mana, making his desire to master all things arcane attainable. Moreover, as the seventh prince of the kingdom, Lloyd has no claim to the throne, allowing him to nurture his abilities as freely as he wants. Unfortunately for Lloyd, ancient seals that imprison powerful demons begin to break down and release the horrors within, endangering the peace. With these monstrosities roaming around, Lloyd's overwhelming magical prowess is the ultimate weapon that can neutralize these threats before all things descend to chaos.