When the player group ventures Ameno Torifune, Ulala Serizawa, Katsuya Suou and Baofu want some place to restore their strength, so Tatsuya does what his former friends did exactly in Innocent Sin by imagining and calling forth the entrances to Trish's healing fountain and Velvet Room. With the group separated, Maya sits by Tatsuya's side and waits patiently for their allies, Tatsuya feels even more depressed for what has happened so far. This strong thought materializes the Metal Trio due to the power of the location being Nyarlathotep's domain. Tatsuya instantly draws out his sword to attack them but to no avail. The three sorrowfully blame Tatsuya for breaking the important promise and teleport away with him, leaving Maya behind. When Maya has regrouped with her friends, they catch up promptly before Metal Jun nearly stabs Tatsuya in the neck. Tatsuya holds the edge of the blade before it cuts his body, the battle ensues.
Upon the defeat of the trio, Katsuya binds wound of Tatsuya's hand. This display of brotherly love unlocks 2 demon contact combos of the Suou brothers.
They first appear in "Room of Damnation", Torifune B5, and kidnap Tatsuya. When the player reaches "Room of Guilt", Torifune B6, Tatsuya will rejoin the group and the boss battle begins.
Because many of their skills are Dark-elemental, Tetraja or item Silver Manisha will definitely help reducing their damage or effect of instant death. The player should focus on one of them one by one, depending on what kind of skills or fusion spells available which hit their weakness hard.
Their battle plays the original boss battle theme from Innocent Sin.
In the Eternal Punishment PSP remake, the boss battle theme does not come straight from the Innocent Sin PSP remake. Instead, the piece is remixed again without the additional second half which contains guitar solo.
Tatsuya fearing his former friends would blame him so giving birth to the Metal Trio is proven wrong if the player chooses the "wrong" dialogue choices in Monado Mandala to awaken Lisa and Eikichi's memories of the other side. The two will blame Nyarlathotep instead of Tatsuya himself and even desire to accompany him to challenge the mastermind once again. This follows the common pattern of rumors which are usually generated from false and negative assumption.