I can clear this up in a pretty straightforward way: 'Surprise Marriage: My Mysterious Billionaire' is not originally a Japanese manga. From what I’ve tracked, it started as a serialized romance in Chinese-language online fiction circles and later got a comic adaptation that people often call a manhua or simply a webcomic. In English-speaking forums you'll see fans casually saying 'manga' because it’s become a catch-all for comics from East Asia, but technically manga refers to Japanese comics, while this title belongs to the Chinese-language sphere.
If you look at the art and text, there are clues. The original panels and dialogue are usually in Chinese characters, and the storytelling style leans into the melodramatic, modern romance tropes that are very popular in Chinese web novels — the secret billionaire, contract marriage, hidden identities, that sort of thing. It’s been adapted into a comic (sometimes formatted vertically for web reading), and there are translations and fan uploads that make it easy to find, but the source remains non-Japanese.
I’ve followed similar titles for years, so I get why people lump everything under 'manga' for convenience, but I like pointing out the differences because the publishing routes, pacing, and even reading direction can change how a story feels. If you’re into contemporary romantic drama with glossy visuals, give 'Surprise Marriage: My Mysterious Billionaire' a shot — it scratches that guilty-pleasure itch nicely.