Pleasant
い adjective
This is a single kanji with an い on the end, meaning you know it's probably an adjective. What's the adjective form of pleasant? It is also pleasant.
This word's reading is pretty weird. We're going to think back to a couple different words to put this one together. The word for heart (心), is こころ. The word for good is よい (or いい, but for this word's sake, よい). A "good heart (feeling)" is one where your heart feels nice and warm and fuzzy (figuratively, not literally. If it's literal, go to the hospital please). That is a pleasant feeling. A こころよい feeling.
彼女の声は小川のせせらぎのように耳にとても快い。
Her voice is very pleasing to the ear, like the babbling of a brook.
快い春風を感じながら山道を歩くのが、とても気持ちよかったです。
It was very pleasant to walk along the mountain path while feeling the pleasant spring breeze.
上司は彼の態度を快く思っていないようです。
The boss doesn't seem to think well of his attitude.
快く引き受けてくれる人がいて、安心しました。
I felt relieved to have someone willingly take on the task.