To become fewer or smaller in amount, number, or degree (an intransitive decrease).
この薬を飲むと痛みがだんだん減る。
If you take this medicine, the pain gradually decreases.
夏になると在庫が減って、店に商品が少なくなる。
When summer comes the stock decreases and the store has fewer items.
年とともに筋力が減る人もいる。
Some people lose muscle strength as they age.