Context: there are rumors Doushirou 道士朗 was in a fight in school. One student confirms the rumor with another.
go-nin mo ita noni attoyuuma ni yattsuketa tte. ５人もいたのにあっとゆうまにやっつけたって。
[Someone said that]: there were five people, and [he] beat [all of them] in a blink.
attoyuuma あっとゆうま
{"a'" to iu} ma 「あっ」と言う間
The span of time it takes {to say "ah"}.
A very short time. Before you can say "ah."
Before you can blink.
aa, go-nin wa yattsuketa, hon no isshun de. あぁ、５人はやっつけた、ほんの一瞬で。
Yeah, five people, [he] beat, in just one instant.
de で Used to mark the time it takes to complete a task. In this case, it takes one instant to people people.
shikamo kan de. しかもカンで。
And using [his] intuition.
de で, again.
Used to mark the instrument, method, or manner something is done. In this case, Doushirou beat five guys in a fight, instantly, and intuitively.
