I recommend a cost-effective nail hardener.

If you want to buy a nail hardener elsewhere, it costs at least 5,000 won, but Daiso sells it for 1,000 won. The brush is soft, and one coat contains a generous amount, so you can just swipe it on. I recommend it to people whose nails break easily or are thin. Applying the nail hardener makes your nails stronger. It has good staying power and spreadability, so I recommend the Daiso Nailed Hardener. The only downside is a distinctive smell, but it disappears quickly.