Angel Beats

 Angel Beats is an anime that was produced in the 2000s and proved itself to be one of the most renown and illustrious animes of all time. Not only was it simplistic in its intent but it had an interesting backstory and story, great character development, and amazing graphic designs for the day and age. And to sprinkle it all off—ecchi scenes and lovable yet repetitive shirt flip, cute girl, and cleavage showing. Although it has its flaws, Angel Beats is nonetheless a great anime and one of the first animes that I watched as a kid. 

 Here's a summary for those interested:

The story takes place in the afterlife and focuses on Otonashi, a boy who lost his memories of his life after dying. He is enrolled into the afterlife school and meets a girl named Yuri who invites him to join the Afterlife Battlefront, an organization she leads which fights against the student council president Angel, a girl with supernatural powers.

Source: https://en.wikepedia.org/wiki/Angel_Beats!