Rainbow Six siege is a good video game to relief stress for many reasons.

Casual and Unranked

Rainbow has many modes two being casual and unranked. In casual you can mess around and play however you want which is better for people that are looking to just have fun, Unranked is more serious and to get you prepared for Ranked, but many people find taking the game more serious better for stress then messing around.

Ranked

Ranked is the most played mode in Rainbow being the most competitive. In Ranked you clime up the ranks as you improve your skills. This is very competitive and is good for people that like competing and will relief stress as you're having fun.

You might thing Rainbow Six Siege is not for everyone but once you try it out you will see how good it is for stress.