一方で【いっぽうで】

一方で means "while", "on the other hand": it sets two things side by side that are both true – two sides of one thing, or two different things at the same time. It follows the plain form; a な-adjective keeps な or takes である, and a noun takes である.

A noun can't take の here.

• × 学生の一方で → 学生である一方で

一方で belongs to writing, the news and careful speech. In conversation, けど or でも does the contrasting.

Starting a new sentence

At the start of a sentence, いっぽう一方で, そのいっぽう一方で or just いっぽう一方 picks up from the sentence before and turns to the other side. Mid-sentence, too, the で can drop.

一方で or 反面

はんめん反面 also means "on the other hand", but only for two sides of one subject. 一方で does that too, and can also set two different subjects against each other.

• × 兄は背が高い反面、弟は低い → 兄は背が高い一方、弟は低い

一方で or 一方だ

After a verb of change, 一方で can be the mid-sentence form of いっぽう一方だ, "keeps getting…". If the second clause follows on from the first instead of contrasting with it, that is the pattern you are reading.