Disclaimer: this review covers two films, both of which were released together in North America by Sentai Filmworks: "I'll Be Here - Past" and "I'll Be Here - Future."
The original "Beyond the Boundary" television anime was a impressive dark fantasy series, it's only major flaw being how forgettable it was. I recall it having a good ending too, with only a couple loose threads not taken care of. My enjoyment of the series made me enter into the sequel movies ("I'll Be Here - Past" and "I'll Be Here - Future") with some anticipation, expecting the story would be a complimentary standalone piece. I was surprised when it turned out to be a direct sequel and conclusion, and despite its flaws, a mostly satisfying one, closing those loose ends and some closure on the romance between the two lead characters.
First, I'll briefly talk about the first film, "I'll Be Here - Past." Aside from a few minutes of new scenes, it acts entirely as a recap of the television series with reused animation. It's a good thing it was made, because my memory of the forgettable series was hazy at best. However, the film stands as one of the worst anime film compilations I'd ever seen. It tries to only show the scenes from lead heroine Mirai's point of view, and as such it skips far too much of the original story, jumping to moments with no explaination or setup. Even though I had seen the original show, I still couldn't understand what was happening in this movie. Even as a setup to the true sequel film that would follow, it doesn't mention the open plot threads: it only adds seconds to the ending when Mirai and Akihito reunite, showing us that the ending wasn't as happy as we remembered. Mirari came back from the dead with little explaination, after all... so it is revealed that Mirai is perfectly fine, but has lost all memories of who she is, including her blood-shifting powers and her time spent with Akihito.
So aside from knowing that Mirai's memories are gone, the first film is entirely skippable. In the second film ("I'll Be There - Future"), Akihito and company make the strange choice to not tell Mirai anything about her past, hoping it would protect her from the fate of her cursed clan and risking her life again in battle. Akihito even tries to actively avoid her as if she had done something wrong. But it is clear from the start that Mirai is helpless not knowing who she is, eventually to the brink of tears, begging her friends to reveal the truth, and any benefit to keeping her in the dark isn't portrayed well at all. It simply seems cruel. The memory-drama makes up about the first half of the movie, before the group has to deal with two enemies from the series still left alive as their final plan is carried out. This is where the story gets easier to invest in: the action is engaging, and the relationships of the villains to the heroes is engrossing. Some tidbits hinting at a larger world and the place of certain side-characters in it make the film an essential piece of world building, even though it doesn't actively explain much of what it reveals. And of course, the drama and romance between the two leads is beautiful to watch, through the emotional tears and confessions.
The art and animation largely carries over in quality from the show, perhaps disappointing given the supposed larger budget of a feature, but the series looked great to begin with. There's less opportuntiy for the visuals to impress on their own, but the animation is strong thanks to the action scenes and facial character acting. Notably, the environments and atmosphere leans more into the dark side: some scenes feature a disturbing worm-like creature that takes over its human hosts, and one scene takes place in a theatrically-rigged abandoned building in the middle of the night. These were clearly influenced by similar works from "Type-Moon," specifically "The Garden of Sinners," a compliment given that said series is a high favorite among anime fans, even though "I'll Be Here" doesn't quite live up to any of those films.
The music is orchestral but not important. The voice acting feels awkward (especially because of how often they refer to their enemy named "Beyond the Boundary," rather than referring to it as a place), but it saves itself during the more emotional scenes where it matters.
To summarize, the story surprisingly succeeds as a satisfying conclusion to the series, despite some strange character choices and its habbit to make more questions than it answers. Truly, you'll have more questions out of the movie than you did going in about the franchise as a whole. But to have a film sequel to a television show be statisfying at all is a rare thing, so I would still recomend "I'll Be Here" to any fans of the original show, whether or not it seems essential prior to watching it. And, thankfully, it is slightly less forgettable than the series to boot.