The first half of the film is pretty straightforward and I think it opens a lot more concisely and to the point than the previous two. It starts with Shirou discovering best boy's corpse, Zouken appears and they talk, cuts to Illya lazing around at Shirou's place and she asks Rin what being an older sister is like/what it means (I don't remember the exact wording, might've been 姉ってどうなの?), cuts back to Rider saving Shirou from Zouken, cuts back to Illya going out to the courtyard and Sakura appears to take her. Sakura defeats Rin, summons Saber to stab Rider from behind who appeared mid-scene with Shirou. Shirou's about to get killed when Illya agrees to go with Sakura so that she'd stop killing everyone and they leave. Illya calls Shirou onii-chan before they disappear and Sakura asks that Shirou does not appear in front of her again, or she'll kill him. Saber goes これは最後の注文です. I think that sets up the direction of the film pretty well. It frames Sakura and Illya as two equally important individuals for this film, and it re-establishes Shirou's moral conflict over whether he's going to save her at the expense of all her victims.
After saving Shirou and co, Kirei takes Shirou to the church's garage to reveal his car and bike and says he'll cooperate. There's a really nice scene of the two in the car on the way over to Einzbern castle and Kirei talks about Kiritsugu and why he hates him. Kiritsugu had feelings but threw them away for his ideals, but got them back anyway by the end. Kirei had none to throw away in the first place, so he finds Kiritsugu quite 不快, but also thinks that Kiritsugu was a happy man. He also asks Shirou whether he's ready to treat Sakura as an enemy. I don't remember Shirou's exact reply but he says he's not Kiritsugu and he will save Sakura. Kirei says you won't succeed Kiritsugu's will, huh (きりつぐの意思を継がないか idr). They arrive at the forest and head to the castle. Cut to Illya in her room with maids. Shirou bursts through the window and complains that Kirei threw him. Shirou and Illya argue for a bit here, Shirou says she's trying to act strong by doing all this and that he doesn't care and is going to save her because he's her older brother and older brothers are supposed to save their younger siblings. He holds his hand out for Illya to take but before she does that Kirei picks her up and says they have to leave. They jump down the window from the third floor, this goes more smoothly for Kirei than Shirou as expected, and then it cuts to Sakura going 来たね、先輩(so you came) and summons Berserker to catch them. Then you get the cool running scene where True Assassin chases them through the trees and Kirei stays back to take him on so Shirou and Illya can go.
Kirei-side, he lures/got lured by True Assassin into the warehouse/church in the forest that you'd recognize from fate route and he monologues about his motivations as he fights True Assassin. There's some pretty cool framing of the church's statue of a saint lady holding a baby as Kirei narrates how he finds enjoyment in the suffering of others or something and how he recognizes it's not right, and that he tried to mend this and even took on a wife. You see a flashback to his wife on her death bed who tries to prove Kirei wrong by stabbing herself, before it cuts back to Kirei getting Zabaniya'd but that failed and Kirei restrains True Assassin long enough that he could go to the roof to 'kill' Zouken. Ends with Kirei narrating that no, the wife was wrong. He was sad because he couldn't get to kill her himself.
Shirou-side, the two hide in a trench Berserker formed while rampaging around the forest and Shirou throws his jacket away (seriously, if they're going to return to the base VN design for important moments like Shirou vs Archer in UBW, or this, then why give him the jacket redesign in the first place). Illya asks why Shirou has to suffer so much when he's done nothing wrong, he says that he has done his share of bad things, but thanks Illya for caring. He jumps out from the trench and unveils the Shroud of Martin on his arm. The following metaphorical scene of Shirou struggling in the wind until he sees Archer's back and Archer goes ついて来れるか? is preserved in its entirety complete with an arrange of Emiya and I'm really happy about that. Shirou regains his vigor and goes おまえこそついてきやがれぇえええ and runs past him and it's perfect. He does the Nine Lives Blade works thing (that CG of him holding Berserker's stone slab sword was reproduced perfectly too) and you see 8 cuts on the ground before he does a final 9th stab at Berserker. You actually hear Berserker say 'you protect her now' (i dont remember the exact line sorry, maybe it was お前が守れ) which surprised me because I don't remember if you ever get to hear his normal voice in the VN. Saber appears.
Cuts back to Kirei meeting Sakura. Kirei mentions how she's more relaxed now, she says she's not the powerless girl she was anymore (her gestures here are like really relaxed and cute, she puts a finger to her lips and ponders over it and everything idk how to describe it well), but Kirei goes nah, there was no difference between the regular you and this power hungry version. Angry, she fucks up his heart and then summarizes the plot of F/Z in like three sentences by mentioning how he's been living through the grail mud after he had died during the 4th war or so on, how Archergil was connected to that or something and that since she's ingested Gil she could fuck him up. Then she feels pain from Berserker's defeat filling the grail. Back to Saber, she withdraws and tells Shirou he's lucky because Sakura's called for her, then takes that back, it wasn't luck, he earned it (i dont remember the exact phrase she used here or if that actually means that she says he's earned this victory sorry, it was like 水からの勝利 or something, idk). It feels like this is the halfways point of the film, probably.
Shirou has a dream of swords coming out of his body and then wakes up at home struggling. Rin's there and recovered, so they and Illya head over to the Tohsaka manor's secret basement to reproduce Zeltrech's sword. On the way Illya explains stuff about the war, how the masters being involved is just a front and actually the heroic spirits are what mattered, and about the Einzberns summoning Avenger in the 3rd war and how that fucked up everything. She explains what Avenger, Angra Mainyu is too. At the basement, Illya and Shirou talk a bit more before she unravels the Shroud a bit and Shirou sees a flashback of the 3 families and Zeltrech on their way to some basement/cave to perform the ritual. Each head explains what they're contributing to the ritual, Shirou sees the sword and the flashback ends there. Rin's back at the Emiya household and Sakura's shadow/projection appears to talk to her for a bit and Rin says she's going to kill Sakura for sure. Sakura says she'll be waiting at that cave that's important in all the routes. Sakura-side, she laments stuff for a bit at the cave with the greater grail (illya explains about the greater grail too i think) and True Assassin appears and you hear Zouken's voice instructing her to make a contract but Sakura kills True Assassin and then extracts Zoukenworm out of her body and crushes him too. She wonders what she'll do after this and Saber tells her that they'll be coming for her soon, there's still that. Sakura says to let nee-san pass, Saber asks what about Shirou, Sakura doesn't have a reply to that, Saber sees that hesitatoin and leaves.
Back to Shirou, he's struggling in bed at night and Rider appears from beyond the door and asks if he intends to be Sakura's enemy. Shirou assures her that he'll save Sakura, he's always been by her side and there's someone he has to defeat (倒す) in order to achieve that and Rider agrees. iirc this originally had choices where the wrong reply would have Rider kill you and what Shirou said this time iirc was the right option? Shirou, Rin and Rider are about to leave the household to confront Sakura for the final battle (theres a cool montage of shirou's daily life with sakura as he makes his way to the 玄関 and he narrates how wow, sakura really meant a lot to him). Before they leave, he offers Illya to continue living with him like before if she has nowhere else to go, she asks him to crouch down and she headpats him and tells him he has to bring Sakura back by dawn.
They enter the cave and meet Saber. She goes りん and does this neck gesture thing that tells her only she's allowed to pass. There's a scene with Rin talking to Sakura, but then it cuts back to Rider and Shirou preparing to fight Saber. There's a very short flashback to Rider and Shirou discussing strategy and he mentions something but you don't get to hear it, and Rider goes that might work. Then the fight begins properly. Eventually Shirou uses Rho Aius to block Excalibur and Rider's pegasus knocks Saber away. Before Saber could get up, Shirou jumps in and stabs her. You get the same pose and angle as the original CG but it's not as dramatic or slow as I remember how it was I think, he just stabs her right away. He thanks Saber for everything and goes on ahead after telling Rider to catch up.
Rin and Sakura's fight was petty much as I remembered in the VN too. Rin goes 'so? i dont care. i never thought my life was easy', Sakura gets angry and tries to burst Rin down but Rin throws the sword to nullify everything and jumps at her. You get a flashback to Sakura and Rin playing poker at the Tohsaka mansion as kids and Rin had a way better hand but hesitates to reveal it to Sakura because she looked so happy with the pair she had in hers. Rin goes ああ、駄目だ and couldn't stab Sakura. She falls over and Sakura realizes what she's done wrong. Shirou appears and there's an action scene of him trying to reach her as the ribbons try to intercept him and she shouts how she shouldn't be saved (私は一人で死にます。私を助けちゃいけない). At this point Shirou already has swords sticking out of his body a little. He reaches her, tells her he'll save her anyway, projects Rule Breaker and she accepts being stabbed. Sakura loses consciousnes and her clothes, but that chibi golem-like imaginary number magic of hers turns into some kind of cloth to cover her. Rider comes and Shirou tells her to take Tohsaka and Sakura away and gives her the house key. Here it's really cool how his lines stumble trying to say Rider's name, almost like he's forgotten it or like he's bugging out, iirc this is also how it was in the VN. Shirou sees how the greater grail hasn't stopped yet so he makes his way over and meets Kirei at the end. The fist fight was pretty good, they moved some of the conversation from before the fist fight to during it but I don't think anyone can say it's not loyal to the original. Kirei gets injurd by punching Shirou and goes 'what a troublesome body, the one who attacks gets hurt instead'. Shirou does not narrate that 'it turns out I like Kotomine Kirei, I was trying not to realize that' or 'he was only doing this because he knew no other way to live' which disappointed me, but he does narrate that they're both sinners and he says 'of course you wouldn't back down. sorry for wasting your time' and kirei goes 'that goes for both of us' or something to that effect (i'm almost certain he doesn't say お互い様だ because i was waiting for that line but he says something that had the same effect). The fight ended the same way as the VN and you sorta get a recreation of Kirei's final CG where you don't see his face.
Shirou heads to the greater grail, he's about to project something to destroy it but his hands shake and he hesitates. Illya comes in in her Dress of Heaven (sorry i dont remember if thats what it's called) and walks on air to head over to the grail. Shirou tries to stop her but he finds himself unable to even remember her name. Illya goes it's ok, you want to live right? Shirou hesitates/struggles but he shouts out 生きて いたいんだ! (I want to live!) She goes 'You said older brothers should protect their siblings. Well, I'm your onee-chan.' Here Shirou finally remembers Illya's name and shouts it repeatedly. Things white out, you see Illya rushing to her mother and then you see Shirou's spirit transform into some ball thing.
Epilogue starts with the exact same shot at the archery dojo as HF1, but with Sakura instead of Shirou. Here it kinda baits you into thinking it's Normal End because you kinda get this hint that Shirou's gone (taiga goes 'when will he come back...' or 'where did he disappear to', its one of those lines, i'm sorry i dont remember which). Rin's waiting outside the dojo and they walk and the film does this thing where it shows them walking down the street and the background keeps changing to a bunch of different places, probably different countries but I mean it's all like, streets with stores that look kinda western but Japan kinda has those too so I'm not sure? You see Rin and Sakura's hairstyles lengthen to the point that they look like their VN selves in the epilogue. You see Sakura cooking alone in Shirou's kitchen, then it cuts back to that walking thing but they enter an alleyway and they pass by TOUKO (no dialogue though you only see her from the back), they open some box and see a fake body and they hold up a bird cage that's glowing and that's supposed to be Shirou's soul I guess. Cut back to Sakura cooking and now Shirou's next to her. They walk out of the house along to follow Rider and Taiga. Rin's there and she asks Rin, ねえ桜、しあわせ? They all make their way to the flower viewing party as Aimer's song starts playing because the sakura's on full bloom, you see most of the cast there, you see Mitsuzuri getting freaked out by Rider's presence and Issei's there, and you see the baka trio from hollow ataraxia with Rin. Sakura's standing outside the park watching all that going on, Shirou comes next to her, and together they step forward.