QUOTE(HikaruScans @ Sep 8 2022, 06:00)
Yeah, that was what I also thought, but it still doesn't click with me.
I won't like it directly since it's on the ex hentai side of the website, but it's called "Koneko Tengoku" by Edogawa Shundei. The story in question is page 15-32. TW: Lolisho
On page 22 there's another example of the boy saying 「じゃボクどー(う)したら」. On 23 he says 「ドークツ (どうくつ)」. It's probably meant to show childish pronunciation, but the important thing is that this indicates that もー→もう is a reasonable deduction for the line in question. 盛大に転んだ is also normal thing to say, so that interpretation now seems like quite a good bet.
If you'd rather not put a link, please consider adding the title and author when you post a question. Being able to examine the art surrounding the text in question, as well as other parts of the work, can provide a lot of clues.
This post has been edited by rinruririn: Sep 8 2022, 05:22