Adventures of an Undead Who Became Paladin is a Manga/Manhwa/Manhua in (English/Raw) language, Manhua series, english chapters have been translated and you can read them here.
The Summary is
“Humility! Integrity! Compassion! Valor! Justice! Sacrifice! Honor! Faith!” He’s a lich, however, he’s knightly! He is a lich, but he keeps his faith in the light! “Fearless in the face of the enemy! Loyal and upright, he fights to the death! Why you may ask? Because protecting the weak is not against the law of the world!” ……………. This is the story of a cat with a bad mouth and a lich who gave his body and soul to the service of the Light!