スイスイ
suisui

To-Adverb

1. lightly and smoothly (of movements); swiftly; glidingly

Onomatopoeia
ヤンマがすいすいと みず うえ すすんでいた。
yammaga suisuito mizunōeo susunde ita.
The dragonfly was skimming across the water.
To-Adverb

2. (progressing) smoothly; (solving) easily

Onomatopoeia
Other forms: