All hail Marisbilly Animusphere! Visionary of Clocktower, unrecognized genius within 12 lords, the ONLY magus smart enough to realize you can't research the root if the world goes kaboom.
What a year it have been, from Sakurai to end with Meteo, from the urban sin-filled Shinjuku to the mysterious Salem. Another harsh year pasted for Chaldea crew while they deal with issues while wiping the clock tower's butt.
By the way the Clock Tower F***ed up again, not that this is news, since within the three pillars of Mages, Clock Tower is at pretty much the bottom of the barrel, with an intelligent lord ratio of 2/12.
(one being Waver, the other being Marisbilly).
Anyway, Moonlight/Lostroom, is a prequel to FGO Cosmos in the Lostbelt, so if you don't have a DEEP understanding of Nasuverse ins and outs, and is not up to date with the most recent major Nasuverse events you are not going to understand a thing. So no need to watch this if you are a newcomer. Think of Nasuverse as a game, this is the patch of the latest version, with all the nerfs and buffs, which is incompatible to old versions.
As for the rest interested, here is a plot summary/review (FULL Spoiler)
Moonlight/Lostroom deals with the aftermath after cleaning up the sub-singularities after Romani's self-detonation to defeat Beast 1, with the Quantum time locks restored and Human Order fixed, Chaldea finally returned to the regular timeline as the world outside is no longer an incinerated wasteland.
However, the world still missed a year due to Goetia (Human Order Correction Protocol), in addition, so the Clock Tower with their usual "didn't do anything, but want all the benefits" attitude decide to use the chance of the Animusphere family's chaos over losing their lord again to steal away control of Chaldea and rip it to pieces and sell the remains.
Yeah, the Clock Tower are assholes with no foresight (the fact Chaldea saved their asses multiple times in the past 2 years seem to be completely ignored in their fit of greed and arrogance), unsurprisingly. Luckily Chaldea is bought entirely by another unknown magus family entirely before this plan came into fruition, and as a result, they are planning to welcome the new director to Chaldea. This is where Moonlight/Lostroom began.
The timeline within the OVA, seems weird, but it is actually very simple, if you understand what is happening.
Moonlight/Lostroom is a special room in Chaldea that is said to show you what is lost, and basically conducts therapy on those who enter it. (Also seem to function more powerful to those who have high leyshift adaptability, we'll get to that)
As a result, majority of what happened is a dream-sequence, only two things is real, Ritsuka entering the room and everything after him leaving.
The first part before he enters is a dream sequence of Olgamary, who after getting tossed into Chaldeas and incinerated, might have fused with it and became a higher being (at least I am 90% sure it is her, plus we are missing Laplace). As a result, she doesn't really realize she is sort of dead and her dream-sequence consists of knowledge that should only be known to very little, and why there is a very cryptic speech from Beast 1 in her dream sequence.
Besides background knowledge on Chaldea's formation and important devices, the most import part is Goetia/Flauros's discussion with Olga. He states that the current Human Order, while beautiful is still very fragile, a single mistake from the current humans could end it all. He (in his own misguided way) tried to remove all the pebbles from the path, and while he failed (lost to Ritsuka and Romani) he believes that there must be more people to carry the burden to face what the future holds. So he asked Olga whether she would choose to become a burden or one who carries the burden or one of the pebbles on the road, before Olga could come up with an answer, Goetia/Flauros's ghost/memory left the room.
Second part, after Ritsuka, enters deals with his thoughts on him position, that even though he have managed to defeat Beast 1, 2, 3-R and the demon pillars, he felt his limits as a regular human that can't be overcome no matter how hard he trains. But decides that what matters most is him giving it all he can, that is what the "Last Master of the Human Order" should do, that he is not defined by his limits but his efforts. This also answered some of Olga's own doubts, therefore she left the room.
The last major part, is Ritsuka suffering from another heavy "dream". As long-term FGO follower should know, having contracts with hundreds of servants and having a VERY HIGH leyshift compatibility (he is basically a mini-throne at this point). Ritsuka suffers from "dreams" a lot, which is sort of soul-out-of-body/leyshift experience, it got so bad at some points that Dante have to routinely enter his mind to clear out some of the debris left in his mind so his soul remain healthy. (I don't think he actually have regular dreams anymore)
This time, triggered by the Lost room, Ritsuka "dreamed" of meeting Galahad(?), who questions his decision on stopping Goetia's incineration plan, stating that regardless of whether Goetia did it or not, Human Order possesses no future,and a burned ruin might be preferred to what comes next. Confused over Glahad's statement, Ritsuka is woken up by the sound of Romani and find himself back in the Lostroom.
Overall, it is a very good prologue to Cosmos in the Lostbelt, and a toast to another year of epic adventures within the sea of time.....as long as Minase is not writing.
P.S. Marisbilly turns out is also a talented scientist (he managed to rope in some fellow cosmic ray physicists into Chaldea), and holds one the 4 remaining contracts with Atlas. Man, can this man be anymore awesome! Kind of explains why the other lords consider him a weirdo/sham, which is so funny. One of the only two smart lords in Clock Tower, who contributed the most to society, managed to create a highly advanced mage-craft and technology organization that can save the world, and could be the closest to actually reaching the root with highly advanced ideas and visions, is looked down by idiots who thought he was a sham.
Once again, I felt puzzled ever since Helena's assassination, why the Clock Tower haven't collapsed in on itself yet due to its stupidity.