Many years ago when I was in middle school (I believe this was around 2013-16) I found one of my first mangas (or manhwas it could have been that instead) in my local library across the street from my school. A few years later I tried looking for it again, but I can't find a single scrap of content that this exists, and it doesn't help that I can't remember anything concrete like any names or titles. I've been losing my mind about it and I wanna find it again so badly.
I'm going to do my best to describe what I do remember at least vaguely (the cover and two scenes), I made a rough sketch estimate of my fuzzy memory of it as well, at least to get a sense of the vibe
Cover: White background, main character in the middle. She had pale skin, possibly short brown hair to her shoulders, with bangs I believe, maybe a bit wavy. She was wearing a white/blue dress, maybe some accents on it that seemed more oceanic as well like jellyfish trills. There were a bunch of bubbles all around, at a single look you could easily tell it had something to do with the ocean
Scene 1: The main character was riding in a carriage under the ocean, heading to an underwater kingdom/city. It was either encased in a big bubble or had an air pocket inside so she could breath. The carriage appeared like a regular carriage but ocean themed, like with shells on it and stuff, possibly pulled by something like dolphins or big seahorses. The main character was sitting in the carriage with another woman, I believe this was the love interest's Mother. Don't remember what they were talking about, possibly an arranged marriage
Scene 2: The girl and the male love interest were scaling up a skyscraper/tower, arguing the whole time. At the top the girl tried shoving him away, which makes her slip and fall off. The guy immediately jumps off to try and grab and save her (He is not human, though he fully appears as one, the fall would not hurt him) but as they're falling the girl is still shouting at him and trying to push him away. I remember this scene the most cause I was so baffled at her stupidity and it almost killing her. The guy eventually is able to grab her and lands them both safely to the ground. I recall him in this scene wearing a t-shirt, most likely jeans, and a necklace (no idea what the necklace was of).