Anime series vary according to the number of episodes and seasons.
Here is the top 5 short anime series to watch:

1- Attack On Titan

The plot of Attack on Titan centers on a civilization inside three walls, the last location where humans still live. Over one hundred years ago, humanity was driven to the brink of extinction after the emergence of humanoid giants called Titans, who attack and eat humans on sight.

2- Dr. Stone

The story about scientific genius Senku and his brawny friend Taiju awakened into a world where humanity has been petrified. Senku and his friend Taiju using their skills to rebuild civilization into its earlier scientific progress.

3- Kimetsu no Yaiba

Widely known as the Demon Slayer, tells a story of a family attacked by demons and only two members survive - Tanjiro and his sister Nezuko, who is turning into a demon slowly. Tanjiro sets out to become a demon slayer to avenge his family and cure his sister.

4- Nanatsu no Taizai

Or the Seven Deadly Signs in the English title, were once an active group of knights in the region of Britannia, who disbanded after they supposedly plotted to overthrow the Liones Kingdom. ... The third princess, Elizabeth, then starts out on a journey to find the Seven Deadly Sins and enlist their help in taking back the kingdom.

5- Hunter × Hunter

The story focuses on a young boy named Gon Freecss who discovers that his father, who left him at a young age, is actually a world-renowned Hunter, a licensed professional who specializes in fantastical pursuits such as locating rare or unidentified animal species, treasure hunting, surveying unexplored enclaves, or hunting down lawless individuals