In their last year of middle school, the five band members of CRYCHIC went their separate ways after an unpleasant disbandment. Each wrestling with their own regrets, the girls enrolled in different high schools, hoping never to hear from one another again. Meanwhile, Anon Chihaya transfers to Haneoka Girls' Academy in the middle of the school year. As most students play in a band as a hobby, Anon desires to fit in and spends her first days trying to recruit members for her own band, envisioning herself as the group's vocalist. She befriends Tomori Takamatsu, a shy girl who seems interested but hesitant about joining. As it turns out, Tomori used to be part of CRYCHIC, an experience that has scarred her deeply. Through Tomori, Anon meets Taki Shiina and Soyo Nagasaki, both former members of the same band. Although Taki detests the idea of playing with Anon, Soyo is delighted to help her out. Now with Soyo by her side, Anon's dream of forming a band is within reach—if only she could find a few more members.

At the climax of the Eve Wars, on December 24 of the year AC 195, the armies of the World Nation and White Fang met in a ferocious battle. World Nation leader Treize Khushrenada was slain, White Fang leader Zechs Merquise disappeared, and Earth was saved from destruction by the intervention of the five Gundam pilots. Having witnessed the consequences of war and hatred, the people of Earth and the space colonies put aside their differences and together founded a new world government. Under this newly-formed Earth Sphere Unified Nation, a year has passed in peace. The government and the populace have disarmed themselves, and almost every remaining mobile suit has been destroyed. Deciding to follow suit, Gundam pilots Heero Yuy, Duo Maxwell, Trowa Barton, and Quatre Raberba Winner place their mighty mobile suits inside an asteroid and send them on a one-way voyage into the sun. But even as they bid their Gundams farewell, a new conflict is drawing near. 

(Source: AniDB)

One morning, at the observation deck of the Bell Tree Tower, a man is suddenly shot dead by an unknown sniper. Conan Edogawa, who happened to be visiting as the murder occurred, rushes to apprehend the sniper but fails to do so. He later learns that the suspect for the incident, Timothy Hunter, is a former member of the Navy Special Ops squad and was already being investigated for a previous murder case. The FBI believes that there are at least three people Timothy wants dead. However, after the deaths of two of them, Timothy himself is killed, throwing the investigation into disarray.

As they lose their only lead, news about the assassinations spreads across Tokyo, leaving the city in a state of panic. It is up to Conan to find and catch the culprit in the hope of putting an end to this sniping spree terror.

[Written by MAL Rewrite]

It is a cross over between the series Lupin III and Detective Conan and takes place after the television special Lupin the 3rd vs Detective Conan. The plot follows Conan Edogawa who sets out to apprehend Arsène Lupin III, the suspect of stealing a jewel called Cherry Sapphire.

(Souce: Wikipedia)