You might be wondering who is Archer’s true identity. Isn’t it obvious?
With Caster finally defeated, Archer is now freed from his master. He decides to finish what he set out to do and kill Shirou. Thankfully, Rin managed to make a contract with Saber so that she can become her master. It’s a big difference for Saber since she is no longer bounded by Shirou’s pathetic source of mana. In fact, she is almost at her full power as she was in the last Grail War. As expected, it seems that Archer was struggling against her afterwards.
Aside from that, Archer finally showed his Nobile Phantasm, Unlimited Blade Works, which in reality is just a marble reality with a graveyard of swords. Still, his true identity is very apparent. Archer is basically Shirou with the same ideals. Given that he was burned by his ideals many times and the very person he saved ultimately betrayed him, he wants to kill Shirou once and for all to prevent that fate from happening again.
With that, I have to admit that Archer managed to be worse than Shirou for the fact that he is ruthless. At least Shirou had some redeeming qualities since he has Rin to keep him in check. For Archer, considering that he despises mankind, he is so far gone that nothing will bring him back to his senses. In short, he is a worse version of Shirou, especially when he has the nerves to kidnap Rin.
Now that Archer kidnaps Rin, it seems that Shirou has no choice but to face Archer himself and settle things once and for all. This makes me wonder, how is he going to do it with so little mana supply? Yep, it seems likely that Rin will have to supply some when he faces off Archer. Before that can happen, Rin needs to be saved. In that case, Lancer offers to help him. This makes me wonder, who is his master and where is Kirei hiding? I guess we’ll find out as the Grail War begins to conclude.
One thing to note from the source is that Heroic Spirits are pulled out of the axis of time and reincarnation, so Archer can’t simply change his fate simply by changing a past timeline where he existed. Also recall that he still tried to knock Shirou out of his ideals earlier in the anime with his words before resorting to his blades. In a way, while he’s hoping for a paradox big enough to rid him of his contract, he just wants to take out his anger on the ideals that betrayed him. You’ll find out more on why Archer despises being a Guardian in later episodes, and possibly some tidbits of what he did as an “ally of justice” before the Guardian stuff if Ufotable decides to expand on UBW with Fate/Extra stuff.
Also to note is that while Archer has been emotionally hurting Rin in every regard, he had her best interests throughout the entire war (one of the bad ends you can get right before Archer “joins” Caster, he sacrifices his life in vain to protect Rin and Shirou from Caster, Kuzuki, and Saber after voicing disappointment in Shirou for making a mistake that cost both Shirou and Rin a chance to survive), especially when he says he planned on Rin making a contract with Saber after he took care of Shirou. When Archer “sells” her off to Shinji, we can kind of infer that he expects Rin to use a Command Spell to call on Saber before she gets raped. He wants her to win the war, after all, with or without him being her Servant. So aside from going to great lengths to commit… uh, suicide, Archer’s just crazily prepared and will do anything it takes to finish what he plans to do, and one of the jokes within the fandom is that he doesn’t have allies, he has goals.
On a side note, it’ kind of funny that Prisma Illya’s OST represents Fate more than this anime’s. The lackluster OST hasn’t been doing the show any favors so far (minus the OP and ED).
Even if Archer wants to try and kill Shirou, I don’t think it’s surprising at all that he still wants Rin to win, even if he is not a servant. It’s already apparent with his secret plan to join Caster just to betray her in the end. Still, I highly doubt he wants to get rid of Rin since his plans doesn’t require that.
Still, I’m curious how the rest of the episodes will play out, especially in regards to Rin finding out that Kirei killed her father in Fate/zero.