Steam
Vapor
noun
Hot water's energy isn't the hot water itself, it's what comes out of it (when it's boiling, for example). This is the steam and vapor.
ゆげ
The ゆ part of the reading makes sense. The げ part for 気 is a bit of an exception, so here's a mnemonic to help with that:
No creature likes steam and vapor more than geckos (げ). Geckos live in hot places, so wherever you see steam, you'll be sure to see at least one gecko nearby, if you look hard enough.
ビエトのおでこから出ている湯気、なんだかいいにおいがするんだよね。
The vapors coming out of Viet's forehead smell nice for some reason.
それ、まだ湯気が立つほどあついから、気を付けてね。
That's still steaming hot, so be careful.
美味しい寿司飯を作るには、しゃもじを使って、湯気が立つ炊きたての熱いごはんに酢を混ぜる必要があります。信じられないかもしれませんが、実際に米一粒一粒を潰さずに酢を混ぜるには技術が必要です。
To make good sushi rice, you need to mix vinegar into steaming hot, freshly cooked rice, using a paddle. Believe it or not, it actually takes skill to mix the vinegar into the rice without crushing the individual grains.