What Is It?
The 2007 Japanese anime (animated) TV show Darker Than Black (Season 1) & the 2008 special side episode Darker Than Black: Beneath Cherry Blossoms In Full Bloom.
Here is how Wikipedia describes this show:
Darker than Black is a 2007 Japanese anime series created by Tensai Okamura. Set in modern Japan, the narrative focuses on how ten years prior to the events of the series, a mysterious spatial anomaly known as “Heaven’s Gate” appeared in South America, shortly followed by the opening of “Hell’s Gate” in Tokyo altering the sky and wreaking havoc on the landscape. During this time, people possessing various special abilities emerged, each capable of different supernatural feats—these are known as contractors. The series follows the exploits of agents Hei and his comrades of the Syndicate organization operating in a post-apocalyptic Tokyo and their mission to uncover the mysteries of the Hell’s Gate.
Here is how MyAnimeList describes the special episode:
A side-story of Darker than Black, also called Episode 26, that takes place during the events of Kuro no Keiyakusha.
The Syndicate has another job for Hei and his team. This assignment involves the sought after possessions of a dead contractor, which are believed to have been buried beneath a cherry tree. Meanwhile, Misaki Kirihara and her team plan a trip to the Cherry Blossom festival.
[Written by MAL Rewrite]