What issue did the Red Lantern first appear in?
Red Lantern Corps
During the Blackest Night event, the Guardians of the Universe are shown observing the War of Light unfolding among the various Corps of the emotional spectrum; one of the scenes depicting the Lost Lanterns confronting the Red Lantern Corps in order to retrieve Laira's body from Ysmault. As the seven Corps battle one another, a new eighth group powered by death is introduced to the DC Universe: the Black Lantern Corps. Black Hand, a leader of the new Corps, releases black power rings that reanimated the deceased in order to recruit members to their ranks.[16] Just as Atrocitus steps into the fight against the Lost Lanterns, the black rings descend on Ysmault, seeking the bodies of Laira and the four deceased Inversions.[17]