Diego holds true to the idea of honor and duty, values imbued by his father who died fighting for Rimtech. He is a natural born leader, a skill fortified by having two younger brothers follow him into military service.
During the opening cinematic, he is in command of a Rimtech survey team whom his two brothers, Jonus and Stefan, are also members of. After a battle with a Hedoth Combot, the discovery of an alien arm by Jonus, and an unfortunate bombing run by Mil-Agro that knocks Stefan off a cliff, Diego remains the only Angelus brother in Rimtechs service. This systematically ignites a war between the three primary corpo-nations, Rimtech, Mil-Agro, and Neuropa, and thus the campaign of Metal Fatigue begins.
As the war starts off, Diego feels increasingly dishonored as he learns of his traitorous brothers; his middle brother Jonus, who defected to Neuropa with his newly acquired piece of Hedoth technology, and his youngest brother Stefan, who was rescued and 'rehabilitated' by Mil-Agro. After feeling incomplete with his brothers gone and requesting a replacement, he is assigned an experienced Combot pilot known as Issadora Toltec. They begin to bond on a professional level but Diego eventually grows dependent on her, and a passionate relationship starts to flourish.
Unfortunately, after several deployments together, Issadora is killed during a Mil-Agro ambush, driving Diego mad with rage. Despite going as far as to disobey orders and being the indirect cause of his superiors death, he is promoted to leader of Rimtech's military forces due to a unique turn of events, and uses his new-found power to track down Issadora's killer, a famed Mil-Agro Combot pilot known as Akiri. After finding him, and nearly killing him, Diego is confronted by Stefan who convinces Diego to spare his friend, while reminding him of his past honorable ways and how he has recently shamed himself and Rimtech. Diego, seeing his old self in his youngest brother, retires from the battlefield.
As the player progress' through each campaign, a log from each brother is kept. The following is an excerpt from Diego's personal log that appears in-game during the events of the first campaign. Each entry contains his name, his serial number (RT1654-CTL7), and a unique number most likely referring to the year (2295) and day (###) of the entry.
New orders forced me to break off the search for my brothers. I found the wreckage of Stafan's Combot almost immediately, but there was no sign of him. No body. No tracks. Maybe someone found him? I wish I knew.
The morale of my staff is pretty low. No one wants to believe Jonus would be stupid enough to join those fanatics at Neuropa, but we all seem to think that's just what he did. Given the poor spirits, I can't believe CTO Hansen is sending us on a milk-run like this. Any competent Combot crew could handle this mission, but instead they send someone with my rank to do it. My staff and I feel like we're being punished for letting Jonus get away with that alien arm. Three months ago they were betting I'd be shooting for the CTO position within a year. No one's talking like that now.
Well, looks like we pulled another milk-run mission. No real challenge here. My staff's spririts remain low.
On the upside, Hansen really came through for me with my replacement second. Issadora Toltec's the hottest combot pilot to come out of Rimtech since...well, since me! She's moved up through the ranks nearly as fast as I have. I haven't seen her since the Three Weeks War, but if she's half as good as she was then, she'll more than make up for Jonus's absence. I don't know what Hansen's motivation was for assigning her to me, but I intend to make the most of it.
Only mintues until we deplot for our mission. I find myself almost hoping for combat. Nothing like fighting side by side to pull soldiers together!
The Board is being cautious. Rimtech has always stood for peace, but I wonder if we really can keep the Alliance together this time.
CTO Hansen is concerned about the new combot tech that Neuropa's been using. He's sure it comes from that arm Jonus found. And now tehre's no question he went over. Hell, Neuropa's been touting his defection all over the comm spectrum. My brother has turned traitor. In my heart I knew he had but I didn't want to accept it. Our father fought and died for Rimtech, and now Jonus has dishonored his memory by going over the Neuropa. He's brought shame upon the Angelus name. Issadora tells me that I can restore honor to the family by my successes. I hope she's right.
My staff is really going to be tested in our new mission. It's gonna be a tight one, as we'll have less than an hour to complete our research in order to make the uplink. A big bonus is riding on making that uplink, and damnit it, I'm going to make it! Maybe a big success on my part will make people here forget what Jonus has done.
A promotion at last! That last mission seems to have turned my fortunes around. And it's in no small part due to Issadora. I expected her to be good, but, damn, she's better than I could have hoped! The whole staff's really come together. There's a confidence there that I haven't seen before.
I've been reviewing the reports of our survey team. The forces that drove them used some tactics that are really unorthodox for Mil-Agro. Instead of a typical massed attack, Mil-Agro carried out a two prong strike, drawing defenses out of position and then hitting their flank. It's almost exactly the same trick I used against MolecTech during the Munich 15040 Uprising last year. Could Mil-Agro have heard about that?
Next mission is to Gamma Sector on Hedoth II. It's a weird place, not even a planet really. It's a metal shell constructed around a large moon. Our archeologists think that the Hedoth built it to be a massive refinery, but no one really knows. Anyway, this promises to be the toughest mission I've seen in a while. The Gamma Sector's been a bloodbath for all three CorpoNations, and I can't see taking it from Rimtech. But, I'm determined to recapture our objective, no matter how many reinforcements Mil-Agro throws in our way.
Now I understand why our enemies have been so succcessful of late! Stefan's with Mil-Agro! Now, like Neuropa, they have an inside line on Rimtech's tactics, and are using it against us. I'm going to have to have to throw out the rulebook and try something unorthodox!
I still can't believe it...Stefan with Mil-Agro! What could have made Stefan join them? They're even worse than Neuropa! As insane as Neuropan beliefs are, at least they adhere to their own code of ethics. All Mil-Agro is about is the Cob family and their wealth. What's happened to our family? How could they betray me like that?!
Worse, my disgrace is not even my own! News of Stefan's leaked, and now all of Rimtech knows that two of the Angelus brothers are traitors! They talk about it when they think I can't hear. Conversations stop when I walk into a room. The Angelus name used to be honorable! Now it is a name sneered and derided!
At least I captured Jonus. Jonus and his Neuropa buddy are in a high security cell and won't be going anywhere soon. Heh, the prison warden is a friend of mine. It told him to put Jonus through hell during his interrogations. We're at war - it's about time we stopped treating prisoners like guests and that's especially true for traitors.
My only solace is Issadora. She's always there for me, on the battlefield and off. She knows my shame and still she does not shun me. She is not blood, but, on my father's grave, she is more family to me now than my brothers.
Another promotion. At last, I'm not just another combot jockey. Not so long ago I dreamed of being a Senior Tactical Officer, but now that I've reached STO status, I'm more frustrated than anything. I've got authority over my division, but I can't make strategic decisions. Rimtech is losing this war, and it's partly CTO Hansen's fault. He's been away from the battlefield too long. He doesn't understand what it's like with all this new technology and enemies with the inside line on Rimtech.
My whole staff has been going on about the New Providence massacre. They're mad as hell and want me to blow Mil-Agro to the galactic rim. I'm all for that, but it's Stefan I want. War is war, and it's bad enough that he's dishonored me by going to Mil-Agro, but slaughtering unarmed personnel, that's unconscionable! Our enemies are no better than animals and deserve no mercy.
Have to deploy in five hours, but can't sleep. Too much on my mind. I should be thinking about the mission, but all I can think about is Issadora. We've gotten so close, closer than I've ever been to anyone. I think she feels the same, but I can't talk to her about it. I can't risk CTO Hansen finding out. He'd transfer her out of my command in a nanosecond. Emotional attachments have no place in war. Well, maybe when it's all over.
Just heard that we've received distress beacons from some crewmen we lost in our last battle! Survivors! Issadora's alive! I knew it!
My people are apparently stranded on Hedoth III, but Hansen won't authorize a rescue mission! "Scarce resources," he says. Damn, Hansen! I won't sit still and leave them to die in enemy controlled territory!
Hansen's got one mission schedule for Hedoth III. GFC Patel's schedule to command it, but I reassigned her and will lead it myself. I'm an SFO and command assignments are within my authority. If Hansen find out, well, he can blow a solar flare.
On approach. Time short. Squad tense. Me too. If any of those Mil-Agro or Neuropa bastards have done anything to Issadora I'll kill every last one of them.
Securebeam Message, To: CTO Bran Hansen RT1311-ALT4, Date: 2295-07-13, Timed Release: 2295-7-14 08:00
My staff is preparing to join the defense force for the Rimtech Board meeting at the Sperry Ridge base. However, our arrival will be greatly delayed.
IntelDiv reports a Mil-Agro incursion at Ice Sanctuary. As you know, we recently captured this Neuropan stronghold and have not finished fortifying our position. I believe this sector to be of vital significance to Rimtech's goals and have decided to engage the enemy. Upon completion of this mission, I will rendezvous at ShuttleHub Delta and continue to Sperry Ridge.
I regret that the urgency at Ice Sanctuary prevent my awaiting your response to this decision
Deigo Angelus, STO, Rimtech 4th Command.
The tightbeam will be ready in a few minutes. Fate has given me new hope. Can it be mere chance that the man who ordered me to abandon my search for Akiri is now dead? Can it be coincidence that I alone stand to save Rimtech from utter destruction? Command of Rimtech is within my grasp, and once I have taken it, honor will be served! I will avenge Issadora, restore honor to the Angelus name, and return to Rimtech to the path of glory. A CorpoNation without honor cannot stand.
Mil-Agro sues for peace, using my traitorous brother as a mouthpiece. Who do they think they're fooling with talk about mind-control and the Cobs? It's all a damned clever trick. They've even offered to pull Mil-Agro's forces out of Ginzee Mesa, leaving Hedoth Prime entirely under Rimtech control. They know full well we can drive them out any time, so it's a meaningless gesture meant to disguise their real intentions!
The Board almost agreed to this insane cease-fire, but I convinced them otherwise. Stefan betrayed Rimtech once, and he's doing it again. That's why I'm going to strike before they can pull out. It'll send a message to my traitor brother, and to all who would dishonor Rimtech and the Angelus name!
I'll personally lead this mission against Mil-Agro. Akiri is among the Mil-Agro forces at Ginzee Mesa, I can practically smell his stench. He's eluded me before, but not this time. Vengeance will be mine.
- Despite the numerical duplication in the log, between missions 7 and 9, that is how it's listed in-game.