This topic (a very interesting read btw) got me thinking - how would I try to dig my self out of that pit if I was a writer for ME3. I did arrive at the scenery that would make me want to talk further with Ash. I don't think it'll work for Kaidan as well, since he has a different personality, but with Ash I can see that.
Show the player what was happening during out 2 years absence (comic or cinematic does not matter).
1. Right after Normandy is destroyed a shocked and grieving Ash is back at the Alliance HQ for debriefing, she is separated form the rest of non human crew her explanations about "big flying rock with lasers" that destroyed the Normandy met with quiet distrust and she can see that people are starting to arrive at conclusion that the Normandy was destroyed by the Geth and it's mostly Jokers fault - a pilot error that allowed them to get close enough without being noticed. Her version of the story is attributed to grief and attempt to help Joker.
2. After Joker is grounded and the debriefings are over Ash is trying to find out what happened to Sheps body, her efforts are met with polite requests to wait and no information, at last she gets an audience with one of Alliance admirals, and he explains to her that he does want to find Sheps body, but the Alliance is not yet ready to officially admit that Shep is dead, for political reasons, not until human position on the council is completely secure, and Alliance can't go and search for the body of someone they are not yet officially consider dead. He does promises Ash that they are keeping the sector secure, and no one is going to disturb neither Shep nor the remains of Normandy until they are ready to officially start the retrieval. He firmly orders Ash to wait and be quiet.
Ash if extremely upset about all thous politics, and maybe even gives the Admiral an earful about how Shep is a hero and deserves to be treated as one, but is forced to back of. Not long after she receives a short, critic note form Liara that is not very informative but lets Ash know that Liara is "taking care of their friend", Ash is still furious with Alliance command but gains some measure of patience.
3. Anderson approaches Ash to talk about the Reapers - after Sheps death everyone gladly forgets about them and goes back to ignoring the treat, Anderson does not believe that the treat is over and thinks that they need to continue what Shep started. That when the time comes humanity will need a leader with a plan, and since Ash was there from start to finish she is the only one qualified to take up Shepsards legacy.
Ash resists explaining that she if not Shep, that she has no idea how he managed half the things he did, that she does not have Sheps charisma, or training, or connections, and she has not idea what to do, but Anderson pushes saying that he wishes that Shep was alive, but he isn't and Ash is the best that humanity has, quite possibly their only chance of survival.
There is no one to take the torch so Ash has to, and she does the best she can, even thou th pressure is killing her, she constantly fears to make a mistake and fail everyone.
4. Ash starts investigating the resplendence of the colonies after Anderson gives her the initial info, of course she hardly believes that some mythical "collectors" are behind it - no one even so one, they are the pirate tails form Terminus system, but every time she gets closer following the trails she encounters Cerberus agents, they claim in what reports she manages to intercept and dialogs she manages to overhear, that they are investigating the disappearances as well, but Ash does not buy it, she knows Cerberus, it's probably them who kidnap thous people for some kind of experiments, or even to build an army or something. She although thinks that this some way is connected to Cerberus largest, and most highly guarded project - Lazarus, and that are strange rumors about Shepard bing involved in it.
5. Anderson learns that Shep is alive and kicking, but he is unsure weather Shep is actually Shepard or some kind of clone cooked up by Cerberus. He is wary and decides no to share the information with Ash until he has a chance to find out more - Ash is under enough pressure as it is trying of fill Shepards shoes, having to deal with some kind of crazed Shepard clone may be too much for her, so Anderson decides to protect her and investigate Shep on his own, he although cautions Ash form punting to much hope in rumors. He believes that Cerberus is involved with the colonies disappearing as well.
6. Anderson and Ash monitor Cerberus and conclude that Horizon would be the nest target, Anderson even manages to persuade the alliance that the colony needs defense and to sends Ash to make sure it's protected. He coroutines Ash that the "Shepard clone" can show up and remains her that she has to be strong, that the fate of the humanity may very well depend on her straight and resolve.
7. Bu the time of her assignment to Horizon Ash becomes to "fry around the edges" - Anderson keeps putting the "fate of humanity" in her hands, and she knows he is right - the Reapers are coming, but she is no closer to figuring out what to do about them than she was 2 years ago, everything that Shep done that looked so effortless when he did it takes the last of her strength out of her - no one believes her, no one wants to help, Sheps allays have no desire to follow her, Liara is busy with something she does not want to share, Tali and Garrus despaired and she can't contact them, Joker dropped of the radar entirely. The galaxy has no desire to see her as the "new Shepard" that they can rail around, even Anderson hides things form her, and she feels like she is stumbling in the dark and there is an abyss nearby...
The Horizon colonists do not see her as any kind of savior or hero, the only thing they want her to do is shut up and go away - much like the rest of humanity at this point. She tries to save them but they refuse to even believe the treat exists. Ash does her best to remain patient and keep them safe... And than the "space pirate legends" hit.
Not only the damn collectors are real, but they are right on top of the unprotected colony, a colony that Ash had to secure weak ago. She is cot in the attack, palisaded and helpless and all she can do is lay there, look at the people she had to save and think. Think about how she did not even see the treat all this time, how she is supposed to "save the humanity" if she is stupid enough to miss something this huge... And a second time around, this is Eden Prime all over again!
And than the main gun, the one she could not get to work for weak starts firing, and the stasis field disappears.
8. Ash stumbles to the center of the colony truing to figure out what is happening and there he is - Shepard. Alive and acting like his usual self - doping out of nowhere to save people from the treat they did not even believe was there, casual and calm like it's something he does every day... And he has a ship, companions and a Cerberus logo on his uniform.
Is he really Shepard, or is Anderson right and this is some kind of clone? If it is him than why did he not contact her? Or does he even need her - there he obviously has a team, and she is not on it. How did he know about the attack? How did he manage to get the damn gun on like so fast? And why no one told her that she may be not "the only hope of humanity" Ash would have been overjoyed to give up that torch, to simply be a soldier, and do what she does best...
She manages to great him calmly, but that's when it all breaks through - the frustration of endless lies and omissions, guilt at all her mistakes - if she only got the damn gun on line it time! Uncertainty and to much pressure for all detections. She snaps and rages at him because at that moment blaming Shepard for everything - for dying, for living her along to deal with his "legacy", for not being convincing enough about the reapers, and most of all for not needing her by his side, and doing just fine without her when she can't seams to make a step without him.
In the end she stormed of even more confused, goes behind the nearest block and does something she never allowed herself to do in all two years - cries. And listens to Shep calling Normandy, the new Normandy, and Joker, who obviously knew but never told her. Shep is busy, he has a world to save and impossible to make happen, what is one crying failure of a woman to him?
9. Anderson does not allow Ash to just walk away - he explains that they can't be sure that Shep is really himself, and that it's not some kind of Cerberus operation, he tells her about Miranda - a ruthless Cerberus scientist and cold blooded operative who is traveling with Shep and watches his every step. And Shepard does not seam to mind. Anderson persuades her that she has to stay strong and be ready to play her role. And that he managed to talk the Council in to appointing her to be a Specter. Ash objects saying that she does not want to get a promotion by stepping on her commanders corps, but Anderson insists, telling her that in case Shep proves to be not who he seams to the humanity will need her, ans she will do the job better if she has the resources of a Specter, and reluctantly Ash agrees with him again.
But instead of truing to invent a non existent way to defeat the enemy she knows noting about Ash uses her new status to investigate Shepard and his activities and the more she learns the more she believes that he is what he seams to be, despite the Cerberus involvement it's clearly Sheps operation. She watches the records, sees the results, talks to people that had contact with him and with relief realizes that humanity has Shep beck, weather they believe it or not.
10. Until Shep goes on trail. For Ash is' the Normandy destruction all over again - no one believes in reapers, no one believes her or Shep, but she knows they are real, and this time around she knows that Shepard is real as well, and if he did what he did he had a damn good reason. Yet he does not trust her, and she can hardly blame him - whatever he went through to come back form the dead was probably much worth than Ash's last two years. She tries to talk to people, soften them up but it is in vane...
And than the Reapers finally arrive. In the panic around Ash makes a decision - instead of trying to "save the earth" something that she, with her track record, is unlikely to do anyway she uses her Specter status to get on board of Normandy and get Joker there as well, she has no permission to take the ship, but in overall panic and confusion it's not that hard, simply showing her Specter status in everyones face works.
11. They pick up Shep and Anderson and something like the following dialog ensures:
Shep: Williams. *courteous nod*
Ash: Commander *nod back*
Shep: Thank you for picking us up. I gather you received the command of Normandy?
Ash: Nope, I stole it.
Shep: I see. So do you mind me asking where re we going?
Ash: It's up to you, sir.
Shep: I'm not your CO Williams.
Ash: Nor formally, no. But I know when I'm in over my head Shepard, the last two years I was truing to fight this fight, to jump hiher than my head, to find a way to stop this all from happeing and you know what? I'm exactly where I started. Because this is not me, not what I do and not what I am - I'm a soldier, not a savior, or investigator, or a politician or some kind of a grate leader - I follow orders, and I'm damn good at it, and if you have me commander I would like to follow yours.
Shep: After our last meeting I was under the impression you do not trust me.
Ash: I never stopped trusting you. I was not sure that you are actually you Sheppard, but I had time to check my facts - even if you are not him you are so damn close that I can't tell the deference... Well you get what I mean... So commander, do you have a use for another soldier?
Something along this lines. Just thought I'd share the idea for the entertainment value if nothing else