I have some issues with the translation for this chapter, I think this chapter might be her first multiple orgasm experience, sonce yira has her first orgasm in chapter 120 and second in chapter 138, not that I would know, I just dont forget things. I will go back and find the raw for this chapter and see what I can find woth loose translations, but it seems to be more about multiple orgasms and not just experiencing it for the first time.
Alroght, so I've gone over the RAW, this translation isn't bad, but I still think we are missing something here. It would appear that yura had 3 orgasms during this chapter, the first two that were pointed out, these were on par with the ones she has been experiencing up until now. The final one in the chapter, is referred to as "iku" in Japanese it's slang for Cummings, so that part is true. However the type of orgasm referred to as iku is also seen as "to go." That the spirit leaves the body as if dying. So this would be a next level orgasm for her.
That's the best I've got, not first orgasm, but first experience with "iku" or next level orgasm. It does translate to Cumming but not I. The exact same usage we associate the slang term.