The Collapse - A Timeline
1.) Shevat manages to form enough of a unified force to strike back at the Sacred Empire of Solaris. Tons of battles, and the like. Krelian presumedly forms the Shevat Shield at this point.
2.) Deal with Gazel Ministry. Decisive battle at Nisan. Sophia's sacrifice. Krelian vanishes, grief-stricken. Lacan is taunted by Miang about how he failed to save Sophia because of his lack of power. We know what the taunting leads him to do.
3.) Contact with Har. Lacan's view of the world and his sadness leads him to believe that the only way to end all the suffering is destroy everything, like Krelian believed. As my friend Nanaki phrased about Lacan: "The saddest thing about it is that he really believes its the right thing to do." Lacan is fractured, but that doesn't really manifest itself, although I bet he takes on the 'Id Look' around here, remember, he looked like Fei/Id in Alpha Weltall's hands before his transformation into Grahf/Lacan.
4.) Lacan returns to Miang, probably to destroy her, and, most likely in exchange for her life, finds out about the plan. Considering that the Gazel Ministry were mainly behind this, he slays the Gazel Ministry to avenge Sophia, but Krelian 'saves' them. Lacan either manipulates beings that are Diabolos or creates the Diabolos and sets out to destroy the world.
5.) Roni Fatima and his friends confront and defeat the 'heart of Diabolos', meaning Lacan. The rest of the Diabolos are trashed. As for Lacan... his friends obviously seem to think they have no choice but to execute him, and take him to an execution site. Remember Lacan's lines in the middle of the wasteland... "Why are you betraying me!?" And, of course ,"Did I... cause this?" However, he isn't able to completely retain his old attitude to the point where he is reconciled, and reverts back to his grief-stricken impulses, transforming into Grahf, which presumedly separates from Lacan upon execution.