muku-muku
Something rising up or swelling in soft, rounded billows — cumulonimbus clouds building, smoke rising, or feelings and motivation welling up inside.
💡A summer sky — 'Thunderclouds are building muku-muku on the horizon.'
入道雲がむくむくと湧き上がっている。
Cumulonimbus clouds are billowing up muku-muku.
Motivation welled up ___ inside me as I watched the game.
試合を見ているうちに、やる気が○○と湧いてきた。