The plot of the story is driven by Shirou, instead of dying at the end of the Heaven's Feel route, becoming a Counter Guardian of Alaya like Archer/EMIYA, and through his presence aims to change things that went wrong. With Kariya as his Master, he will influence many events in the future.
As of October 5, 2016; the story has now been officially cancelled. The author then revealed that he's going to reboot the entire thing into another fanfic called Fate Liner: Red Knight, using characters and elements from Fate/kaleid liner PRISMA☆ILLYA and Fate/Apocrypha as a basis.
Fate Zero: Avenger of Swords contains examples of:
- Adaptation Expansion: There are several scenes that focus on the other servants like Lancer and Rider rather than Saber and Avenger.
- Adapted Out: Lancelot and the Berserker Class, since Kariya summons SHIROU to the Avenger class.
- Ax-Crazy: Caster as usual.
- The Blacksmith: Shirou as usual, though he creates some weapons that are not seen in the main series:
- Caduceus: Normally an A-Rank Noble Phantasm worthy of Hermes, it has been downgraded to a mere C+ due to Shirou's need to trace it quickly to stabilize Kariya's condition. With its legend warped by confusion with the Rod of Aesculapius (blame the Red Cross), it's capable of healing wounds and eliminating illnesses, but it takes time as a result of the transience of the copy.
- Jarngreipr: The iron gloves of Thor that are used to enhance his already monstrous strength. Shirou uses them to punch Gilgamesh in the face hard enough to tarnish his visage.
- Broke Your Arm Punching Out Cthulhu: Subverted. Avenger is left worn, aching, and out of mana from his fight with Archer, but he only managed to land a single blow to the arrogant Servant's face (which is more than enough to damage the Golden King's pride).
- Character Development: Shirou is aiming to give Kariya some, and it seems to have worked but time will tell. More radically, Kayneth and Lancer get some serious character development, but it's going to take a while...
- Early-Bird Cameo: Touko and Daisuke show up in Chapter 4, showing how some things are different.
- In Spite of a Nail: Despite abandoning his old ideals, Shirou still ends up becoming a Counter Guardian. Unlike Archer, though, he only acts for Alaya when his friends or their descendants are in danger.
- Master Swordsman: As per canon, Shirou gains the combat experience of the owners of the weapons he's copying. However, he's still not as good as the originals, forcing him to take several hits during his fight against Archer.
- Meta Twist: In other stories, we never really learn about Shirou's parents. Here, they are Touko and Daisuke from Kara no Kyoukai, which makes a decent amount of sense given Shirou's unusual hair color and magic circuits despite his mundane early life.
- Mythology Gag: Miyu is Shirou's sister, and Avenger uses some of EMIYA's preferred tactics, such as Hrunting from Fate/hollow ataraxia.
- The Reason You Suck Speech: Shirou and Rider hand these out to Gilgamesh and Kayneth respectively.
- Underestimating Badassery: Due to SHIROU being the Avenger class of the Fourth War, this is the initial general reaction to him. At least, before the battle with Gilgamesh at the Docks.
- Warrior Therapist: Shirou tries to be this to Kariya in order to ease his Master's rage and unhealthy psychological condition.
- Weak, but Skilled: This is Avenger's schtick, and his stats are similar to EMIYA's in some respects. However, some of his stats are larger than EMIYA's based on the Heaven's Feel route of trials that Shirou went through.