Leviathan is one of my favourite anime from Summer 2025, and I didn't expect to like an anime whose source material is a recent young adult novel.

Leviathan covers the trilogy of the same name by Scott Westerfeld: 1) Leviathan, 2) Behemoth, and 3) Goliath. It is an alternative retelling of the events of World War I. In that world, there are two major powers battling each other: 1) the Darwinists, who correspond to the Triple Entente, use genetically engineered creatures for battle, and 2) the Clankers, who correspond to the Central Powers, use mechanised walkers.

Note that even though this is an anime about war, it's not about it entirely. It's about the 'bromance' between Prince Aleksandar and Dylan Sharp and how their actions affect the outcome of the Great War.

One does not really need to be knowledgeable of World War I, though it doesn't hurt if you do, to be able to appreciate this anime. It's an historickal fiction, and thus the author, Scott Westerfeld, took liberties in representing certain historickal figures in a good or bad light. Some characters are a fabrication of the author's imagination. For instance, Prince Aleksander is the son of Archduke Franz Ferdinand of Austria in the anime. Prince Aleksander, however, is not an historickal person.

It's also not necessary to know why they went to war because the story will tell you its own version as to why these powers went to war.

The differences in worldview of the Darwinists and the Clankers reflect the differences between Britain and Continental Europe, an example of which can be seen in the differences between Analytick Philosophy, which values lucid prose, and Continental Philosophy with writings filled with gobbledygook, at least from the point of view of the uninitiated.

And before I forget, the synopsis of the anime and the novels tells us that Dylan is actually a girl named Deryn Sharp. This continues the tradition of cross-dressers in anime; the chief example is The Rose of Versailles.

It's not a documentary. It's a war story that is only successful if you are moved or not. The point is to entertain and/or move you emotionally. Leviathan succeeds in having you immerse yourself in the world of the characters and being sympathetic to their struggles. Alek and Dylan belong to different social classes, yet they have a common humanity, which the anime is able to convey, and that's why it advances the idea that friendship transcends class, nationality, and other arbitrary differences.

Speaking of the mood, both OP and ED, which are composed by Joe Hisaishi, leave you emotional. In the opening, titled Paths Combine, it's just an instrumental, but has a vocal version in one of the episodes. It serves as background musick to heighten the emotionality of the scene. The ED sang by Lady Diana Garnet is just great. It's an emotional song that serves as a desert after an emotional episode.

If there's a downside, the animation is not as smooth. The characters appear to be 3D, though not to the point of being like CGI cartoons. The movements are not as smooth.

Another criticism is something levelled by fans of the source material. Much has been removed because properly giving the source material its due requires 24 or so episodes. That's why, for them, the anime feels crammed.

But for people like me who did not read the source material prior to watching the anime, I don't see it as rushed. What's adapted is done well. Perhaps if this were given even more episodes, this anime might deserve a higher score.

I had a great time watching this anime. Despite its imperfections, it succeeds in promoting the source material, at least as far as I'm concerned.

NOTA BENE: A grade of 8 out of 10 [or 80 out of 100 in anilist] means that I find this anime is very good and three notches above average. I enjoyed watching it.

My enjoyment spectrum lies from 4 to 10. If I have scored an anime below 4, I actively dislike it.