From BiliBili Comics:
After remarrying, Dad and his beautiful stepmother embarked on a honeymoon abroad, leaving Aunt Qian He, who coincidentally shared the same birth year with San Qiu, to move in. Expecting the start of an unabashed life at first, it never occurred to San Qiu that his aunt was a Demon-slaying Celestial Being. San Qiu himself, much coveted among Demons alike, found himself a constant target by Demons… Not to mention his long-lost childhood friend, Xiao You turned out to be the greatest assassin of the Banished Celestial Agency, an organisation managed by Celestial Beings. Xiao You simply could not stand the sight of Qian He, who came between her and the love of her life…

Original Webtoon

From Macedon Scans:
My father remarried to a beautiful stepmother and they traveled abroad. My new aunt Qianhe of the same age moved into the house. I thought I was going to start a life that I wouldn’t be ashamed of, but I didn't expect my aunt to be a demon-slaying immortal, and I Sanqiu to be highly coveted by demons. Attacks continued... but I was surprised to find out that my childhood sweetheart Xiaoyou, who I haven’t seen for many years, turned out to be the strongest assassin of the Deity management organization “Banished Deity Bureau.” And now she has feelings of hostility towards Qianhe, who she sees as her rival in love.....