- "Any time something begins, inevitably it has to end, doesn't it?"
- — Tsukasa —
Catastrophe is the twenty-fifth episode of .hack//SIGN.
Morganna's screams of anger are heard by Tsukasa, and Bear asks if they should leave. The others agree and head to Mac Anu. BT prepares for the battle while the others move on to Hulle Granz Cathedral. Before she can proceed however, Sora PKs her after being unable to get the location of the others from her.
At the Cathedral, Bear and Crim stand guard while the others head inside. As the two chat, Crim laments that he won't be able to see the entire matter of the hidden force of The World to the end, but is satisfied if he knows that others will rise up to finish what they started. BT soon appears and informs them that Sora is working for the enemy.
Inside the Cathedral, Tsukasa discusses his future and the reason he was chosen by Morganna with Subaru. Subaru reassures him that they will resolve things. Bear, who has switched places with BT, approaches Tsukasa and has a private talk with him. He offers to become his legal guardian in the real world, deciding that he is finally willing to take full care of him. He also acknowledges that doing so would provide him with a second chance to be a proper father.
Outside, Sora appears to settle his score with Crim. BT is unable to help as Silver Knight calls for reinforcements. Inside the Cathedral, a Guardian has appeared to attack the group. Meanwhile, at the old area where Aura once slept, Macha looks at the bed and a shred of Aromatic Grass, wondering what she must do. When Morganna calls for her, Macha displays a look of discontent.
Crim and Sora face off at the roof of the Cathedral while the others challenge the attacking Guardian. As Crim and Sora cross blades, Crim lectures Sora and explains that although Sora's stats are about equal to his, he is stronger because Sora lacks passion. Inside the Cathedral, Subaru gives Tsukasa the choice to leave, so Tsukasa asks Mimiru to cover their escape. However, witnessing the strength of the others, Tsukasa decides to stay behind and help fight. Together, they manage to defeat the Guardian. Meanwhile, Crim knocks Sora off the Cathedral and forces him to retreat.
Although the Guardian is defeated, three more take its place. Tsukasa boldly tells the others to leave while he takes on the Guardians himself. Although he is resolved to battle them himself, Macha soon appears, holding a blade of Aromatic Grass with her. Upon seeing Tsukasa, the blade of grass grows. Pleased, Macha resolves to take the place of Tsukasa as Macha and the three Guardians simultaneously Data Drain each other. Although Macha and the three Guardians disappear, Tsukasa, Subaru, and Mimiru are all warped to a different area by Morganna.
- This episode reveals the relevance of Aromatic Grass.