You will not be charged during the free trial period.
Keep in mind, however, that once your free trial has ended, it will be renewed as the paid plan you selected when you signed up. Once your paid plan begins, you will start being charged automatically.
If you want to cancel your plan before payments start, make sure to do so at least 24 hours before your plan is due to expire. For the steps to cancel your subscription, see this Help article.
Note: You can only use the free trial once with the same LINE account, even if you delete your LINE MUSIC account and sign up again.