* CompleteMonster: [[GeniusBruiser Thiazzi]], from ''Soul Eater'' and ''Oath Breaker'', is the Oak Mage and the most sadistic of the Soul Eaters. Seeking total domination, Thiazzi and three other Soul Eaters attempt to unleash a demonic horde on the human world to subjugate the clans to their will. Reemerging later, [[ManipulativeBastard Thiazzi]] instigates a war between the Deep Forest clans and kills both the Deep Horse and Auroch Mages to impersonate them and [[PlayingBothSides manipulate both sides]]. Using his newfound power, Thiazzi reintroduces dead customs such as cutting off hands as punishment and kidnaps several [[WouldHurtAChild children]] to turn into Tokoroths, a torturous process which renders them [[EmptyShell empty husks]] possessed by demons. Desiring to obtain the final Fire Opal piece, Thiazzi [[HeroKiller murders the young Bale]] to steal it and then tries to manipulate the Deep Forest clans into declaring war on the people of the Open Forest, so he can conquer everything. Thiazzi also takes advantage of a mentally ill woman to use as a servant and orders her to start a huge fire to [[FrameUp frame Torak]] for it and have him executed. He then kidnaps Renn and traps her in a hollow tree to slowly suffocate to death. When Torak submits to his will, Thiazzi immediately [[ILied breaks his promise]] to spare Renn's life and tries to kill them both.
* DieForOurShip: Poor [[spoiler:Bale]].
* EnsembleDarkhorse: Dark, introduced in ''Ghost Hunter'', the originally planned last book.
* HarsherInHindsight: In ''Soul Eater'', when Torak and Renn come upon the Walker again, he is distraught over having lost Narik, and Torak replaces Narik for him with a lemming he grabs out of the snow. The entire episode is awful in hindsight, but especially when one skips forward to ''Ghost Hunter'', and Torak is replacing Narik again -- [[spoiler: by being the second dead child the Walker retrieves]].
* HoYay: Fin-Kedinn abandons his clan (only for a little while but nonetheless) to go off and find the Walker in the ''Ghost Hunter'', and then spends most of the rest of his appearances protecting and taking care of him. He even offers to let him stay with the Ravens at the end, and seems quite disappointed to be refused. All in all, it comes across as very reminiscent of Janet rescuing [[Literature/TamLin Tam Lin]] with the power of her love.
* IKnewIt: In ''Viper's Daughter'', Naiginn's blue eyes and fair hair led some readers to speculate that he had some ties to the Seal Clan. [[spoiler:Those readers were proven correct when his true father was revealed to be Tenris.]]
* MoralEventHorizon: In ''Spirit Walker'', [[spoiler:Tenris]] crosses this when [[spoiler:he reveals that he was [[EvilAllAlong all along a Soul Eater]] and [[EvilUncle the brother of Torak's father]], created the demon bear that killed [[CainAndAbel Torak's father]] in ''Wolf Brother'', created the sickness that he used to kill Bale's little brother just to test it, and killed a young orca whale just to get its teeth (causing its vengeful kin to cripple Detlan). As he reveals this all, he prepares to eat his nephew's heart to become a spirit walker himself]].
* {{Squick}}: In the seventh book, Renn is given ptarmigan droppings to eat.
* WhatDoYouMeanItsForKids: Despite it mostly marketed as children's literature, there is a great deal of heavily described violence and gruesome images, as well as one or two important deaths in each book (also very gruesome and well-described). There is also some sensuality, especially since the fourth book. [[spoiler:And Thiazzi's physical and psychological torture of Renn in ''Oath Breaker''.]]
* TheWoobie: Most of the main characters fall into StoicWoobie.
** Dark, probably the most. His clan was disgusted by him because he was an albino, and the only person who loved and protected him was his mother. When he was eight, his mother died. His father took him deep into the mountains and left him there. The next time he had human contact was when he was fifteen when he met Torak and later Renn.
** Torak loses his father and is tossed into a destiny he was not prepared for, against foes he has no clue how to deal with. Having been raised away from the clans, he's not used to living with so many people, and feels like he doesn't belong with them. [[spoiler:It doesn't help when he is later made an outcast.]]
** Oh, Renn. To start with, [[spoiler:her mother is Seshru. Seshru only planned to use her as a tokoroth, at least before Saeunn intervened. Afterwards, Seshru didn't even bother to see if her daughter survived]]. She loses her father at an early age, and because of her talent for Magecraft, (which she is reluctant to use because [[spoiler:she inherited it from her mother]]) people avoid her. Her first real friends were Torak and Wolf.
** For Fin-Kedinn, his two best friends joined a [[ReligionOfEvil cult]] and disappeared, and the girl he loved married one of the aforementioned friends and died. His little brother also dies, leaving him the sole caretaker of his niece and nephew. The nephew gets himself killed in an avalanche, and the niece keeps getting herself in danger by helping with Torak's quest and so forcing him to run all over the known world to rescue her. The Soul Eaters almost kill him in the first and fifth books. The first book also sees him find out that his best friend has died, which he blames himself for. And in the sixth book, Renn and Torak leave for the other Forest, and Saeunn dies, leaving him with no close relationships left.
** Torak's father accidentally joins the ReligionOfEvil, thinking he was doing good. He ends up having to fake his own death, chop off bits of himself, and commit murder to get out, after which his wife dies and he spends twelve years as an outlaw in the woods. And then his brother kills him. And ''then'', he gets brainwashed right back into being a Soul Eater again.