Act IV: Lone Wolf Arc
The former child soldier of an otokonoko finds himself waking up in an art classroom--far away from the site of his battle with the now-deceased Officer Cadet Terrence Denel. Yuki recalls the moment where the 'sister' he cared for--Miyu Shinohara, murdered Denel when it was clear that Denel didn't even want to kill him (Yuki). The trappy agent of Defense Intelligence HQ curses as he screams at the top of his lungs and slams his right fist against an art stand--violently knocking it over.
At this point, Yuki begins to recall his mother's initial deception, followed by his near-death during the 'Child Soldier Uprising'. These two flashbacks are followed by the visions of Naomi's 'murder' of Seiko and Miyu taking the life of the Officer Cadet who was once his (Yuki's) comrade. Yuki Shinohara, seized by rage, declares his mother Sayaka, onee-chan Seiko, former love Naomi, and now his twin 'sister' Miyu, as enemies--swearing to himself that he will erase them for their 'manipulation' of him. Taking up his armament once more, the now-deranged straight trap embarks on what amounts to a rampage in Tenjin/Heavenly Host--killing anyone that gets in his way.
Throughout Yuki's rampage, Sachiko Two tries to contact him via radio multiple times, but is ignored. After so many calls, Yuki angrily answers the call, replying to his concerned friend "Is the NTW-20 ready?" The elder of the Shinohara Twins is even more enraged when he finds out not only did Sachiko Two not complete the weapon's 'counter-paranormal conversion', but also refused to in realization of his state of mind. This leads to Yuki finally bringing out his initial accusation of the tentacle girl having ulterior motives in regards to his 'reanimation', which she at first denies.
Realizing she can't hide the truth from him anymore, the tentacle girl clone of Sachiko Shinozaki informs the enraged fem-boi that the reason his heart and right arm were hurting was because his siblings harvested those very same parts from their corpses to transplant onto him. This leads Yuki Shinohara to realize that the heart beating inside him is Seiko's and his right arm Miyu's. Although this calms down Yuki somewhat, it also confuses him as to why his one-beloved sisters would do such a thing. He is even more horrified when he learns Seiko and Miyu cremated their own corpses following his resurrection as a 'sentient zombie'.
The radio conversation ends with Sachiko Two forgiving Yuki over his outburst, but Yuki himself begins to feel guilty over the actions he's taken in Tenjin. He realizes that what Seiko said was true--that he wasn't even trying to abandon his past as a child soldier--choosing to retain the way of the 'gun and knife' instead. As such, Yuki Shinohara loses the will to fight completely--forcing him to evade New Humanity's forces as they continue to hunt him down.
Eventually, the terrorists in question find and corner Yuki, leaving him with nowhere to run. He first hesitates to draw his gun (whichever Yuki is currently equipped with), but when a warning shot comes close to the right side of his head, he instinctively responds with a Flashbang that blinds his pursuers. By the time the flash subsides, we find that our trappy protagonist had killed the terrorists in question with rage-filled gunfire.
The former child soldier otokonoko then hears slow applause come from his left, prompting him to turn in that direction and aim his weapon that way. He lowers the gun when he finds himself looking right at a certain boy wearing a sleek black, high-leg leotard under a matching miniskirt and a flak vest with detached sleeves to match. This auburn-haired fem-boy, who also wears a jet-black beret, wears massive, mechanized boots with built-in tank-like treads to enable 'skating' over terrain, shoulder-mounted shields, and what appears to be a heavily modified M61 Vulcan with short barrels for CQB use. Like all of the trappy child soldiers' big guns in this series, this particular Vulcan is held left-handed.
Yuki Shinohara manages to identify this person as his former CO and the leader of the Child Soldier Uprising--Colonel Vincent Thorne. Yuki angrily confronts the Colonel over the events of that day, asking why the Uprising was stage in the first place. The Colonel remarks that Yuki had lost all sense of his 'upbringing' in the unit and had reverted to the old ways of 'parental slavery'--adding that it "makes me (Col. Thorne) sad to see one of my greatest men fall so far". He then offers Yuki a chance to rejoin with those he "belongs with", with Yuki replying with the threat to kill the child soldier Colonel for using him--just like everyone else he thought cared for him. Sighing, Vince brings his 'Shorty-Vulcan' to bear and the two fight.
Boss Fight: Colonel Vincent Thorne (1st Encounter)
Incidentally, Colonel Vincent Thorne shares the same boss theme as Vince from Metal Gear Acid 2--as if this game weren't more Metal Gear than Corpse Party enough.
This is one of those boss battles that are really there just for storyline advancement (Read: Yuki is defeated no matter what), and it doesn't help that our trappy protagonist is out-gunned here too. Like with the second and final fight with the late Master Sergeant Erich Wolfe, approaching Thorne from the front is suicide--that Vulcan will kill Yuki in no time. On top of that, Thorne's shoulder shields also protect him from flanking and rear attacks, so Yuki is forced to survive with no chance of taking his former Commanding Officer down.
During this fight, Yuki and Vince trade verbal stabs, with the latter reminding the former that his parents were so abusive that in order to "win his freedom", he feigned a suicide attempt to attract his parents--only to murder them in cold blood. That's when he ran into an agent of New Humanity and willingly volunteered to not only join them--but bring their dream of a humanity devoid of age discrimination against the young did not exist. Yuki replies with the belief that he (Vince) allowed himself to be duped by New Humanity just like himself, and that as a result, the both of them became children of death--destined to go to Hell for the sheer number of lives they've taken.
After some time passes, Yuki finds his heart and right arm hurting, hindering his ability to fight. It's at this point that Colonel Thorne reveals he was the one who commissioned the creation of the cyborg ninja Miyu Zwei as a 'replacement' for the Lieutenant. Yuki-kun drops to his knees as the pain in both heart and right arm intensifies while the Colonel lowers the Vulcan carried in his left arm via support rig in favor of drawing the P90 stored in his right leg compartment--said PDW in his right hand. He takes 'compassion' for his former comrade, promising him release with the intent of putting a 5.7mm round in the Lieutenant's heart, only for a series of tentacles to burst out through the ground and cut the Colonel off.
Yuki Shinohara recognizes those tentacles as the same ones that killed him earlier, but tries to shake his doubts about them as he takes this chance to pull back into hiding. With his former CO stalled, Yuki-kun radios Sachiko Two to report a 'wall of tentacles' that had just saved his life--asking if she was the one who deployed them. When the tentacle girl denies this, the elder of the Shinohara Twins realizes the one who saved him was...