This page of the FF7 Remake guide has a description of Paying Respects side mission, available in Chapter 8 - Budding Bodyguard.
Find a concerned man standing near the weapons merchant. Talk to him, and he will tell you he can't visit his wife's burial site. You must purchase a key at the Moogle Emporium in children's hidden camp. That way, you will be able to unlock the door to the cemetery and fight the beasts.
You will face Venomantis which can poison you and cast Sleep. You have to watch out for their special attacks, block and counter them, and use Cloud's and Aerith's abilities. Aerith is very good at dodging attacks - order her to heal Cloud. After that, go back to the man and tell him the cemetery is safe.
Reward: Studded bracer (has 40 Defense, though only 10 Magic Defense).