how does buffy come back in season 6
Buffy the Vampire Slayer (season 6) At the beginning of season six Willow resurrects Buffy with a powerful spell. Although her friends believe that they have taken her out of Hell, Buffy had actually been in Heaven since her death (a fact that is revealed to her friends later in the season). She is therefore traumatized by her resurrection and this causes her to fall into a deep depression for most of the season.
Spike (Buffy the Vampire Slayer) Spike returns to Sunnydale alone in Season Four, in the episode "The Harsh Light of Day", briefly living with Harmony Kendall, a shallow former classmate of Buffy, now a vampire.[16] He is in Sunnydale to look for the Gem of Amarra, a ring which makes a vampire effectively invulnerable. He finds it and attacks Buffy in daylight, but she wrests the ring from his finger and sends it to Angel. Spike goes to Los Angeles, and hires a vampire named Marcus to torture Angel in order to get the ring, but Marcus takes the ring himself and Angel finally destroys it.