Death Note is one of the most popular manga series of all time with a massive following both in Japan and other countries. The anime was similarly well received and still has a large following to this day. The characters' calculated moves and the overarching plot plays out like a brilliant game of chess, and the story is known for being one of the smartest stories in a manga or anime.
While the anime follows the manga pretty closely in regards to the story, there are details that are left out in the anime, especially regarding Light, the series' main protagonist (or antagonist, depending on your viewpoint). It's nowhere near as drastic a change as the questionable Netflix adaptation, but there are a fair amount of details that fans who've only watched the anime would miss out on. Beware, spoilers ahead!
10 Light Isn't Spiteful
The anime immediately portrays light to be a bit of a spiteful person. In the first episode, he's openly listening in on his classmate's chatter and throwing looks of hatred or disgust at them. Even when the teacher calls on him to answer a question, he first audibly sighs.
In the manga, Light was still more to himself but wasn't nearly as spiteful. One detail that people might miss is that Light isn't hateful—he's just bored. His facial expressions are very different in the manga. He's not mad at the world, he just doesn't find enjoyment in it because he sees himself as so much smarter than everyone around him. He even flaunts this somewhat by bragging about his grades and his ability to reach the Director of the National Police Agency. He's mainly a hyper-intelligent kid who isn't satisfied with the world, but he's never portrayed as being bitter.
9 Light Thinks The Death Note Is A Funny Joke
In the manga, Light's main reaction to discovering the death note is pure amusement. He's smiling as he picks it up and even openly laughs a number of times. The sense of fascination is still there, but manga Light mainly sees the notebook as a funny or strange device that might make his life a little less boring.
Even when reading the rules, he does so in a lighthearted tone, still laughing a bit about it. Light has a sense of humor, something that people who watch the anime wouldn't see much at all of. The main takeaway here is that Light wasn't actively hoping that the Note would work and instead found it an amusing retreat from the monotony of his day to day life.
8 Light Wants To Throw Away The Death Note
Immediately after using the death note the second time and stopping the group of motorcycle thugs from potentially sexually assaulting a random girl, he thinks about what he's done. When he actually kills the leader of the gang, he's openly horrified, and his first thought is to get rid of the death note. He even reaches for it to throw it away before stopping himself.
This is a subtle but important detail in Light's development because it shows his sincere hesitation in taking on the responsibility of passing judgment. For some reason, they skip over this detail in the anime, portraying him instead as someone who is ready to take lives.
7 Death Note Takes A Toll
In the manga, Light suffers some physical consequences from his first using the death note. He explains that for five days he couldn't sleep, was having trouble eating, and was generally losing his mind for a bit. This resulted in him losing weight because he had no appetite. The killing of people takes a serious toll on his mental state much more than in the anime. This detail shows just how unexpected and harsh his decision to cleanse the world of criminals affects his mind.
6 He's Not A Loner
The anime makes it a point to show how much of an isolated life Light leads on a daily basis. Many of the shots are him by himself (e.g. walking to school alone, eating lunch alone, and not playing sports with his classmates).
However, Light wasn't like this at all in the manga. He's portrayed in the manga as being very popular, and Takada even mentions how he's the talk of the school and how all the girls like him. He's shown to have very high social skills in the manga. He's also good at everything; he's friendly, he's intelligent, he's a lady's man, he's a hard worker, and he's an excellent athlete. He's a perfect human with a rising sense of discontentment because it's all so easy to him.
5 Light's Birthday
A little-known detail about Light is that his birthday is February 28th, 1986. This might hold some symbolic significance. His birthday comes a day before February 29th, a leap day that only happens once every 4 years. Whether or not this was taken into account is unknown, but his birthday is nonetheless never revealed in the anime. Pisces rejoice, as you share your symbol with one of the greatest manipulators to ever exist.
4 He's Smarter Than L
Though some claim L to be the smartest character in the series, in Book 13: How to Read, it specifically lists character attributes on a variety of different scales. L is rated on things like Intelligence, Sweet Tooth (maxed out, of course), and Sociability, while Light is rated on Intelligence, Acting Skills, Creativity, and more.
Light achieves perfect scores in Acting, Emotional Strength, and Social Skills and scores a single tic higher in intelligence than L. Fans will still debate, but it's pretty clear in "The Ultimate Death Note Encyclopedia."
3 Light's Eyes
This is a subtle detail that wasn't nearly as pronounced in the anime as it was in the manga. It's shown most clearly in a flashback near the end when Light recalls his first conversation with Ryuk, as well as when he loses his memories in jail.
Before Light obtains the death note, his eyes are much more open and innocent. They're tall and bright. They're drawn specifically to showcase the transformation to come, and, when we return to the present, we see just how much Light's eyes have narrowed since then. It's a small detail that highlights the Death Note stealing his innocence and making him more distrustful and, ultimately, evil.
2 Light's Weakness
It's clarified in the manga that Light would never have lost to either Mello or Near if they hadn't worked perfectly together. Mello was forced to knowingly forgo his life to ultimately beat Light, something their predecessor L was unable to accomplish.
Light is so clever that they never really make a weakness obvious for him, but it can be inferred from the events. In the manga, they specify that Light's ultimate weakness, and what led to his downfall, is that he never doubted himself or his abilities.
1 Light's Downfall
His ultimate death is very different in the anime and manga. One detail they drastically changed was Light's pleading to Ryuk. In the manga, Ryuk is standing behind Light the entire time in the final showdown. Near even says hello to him, proof that he knew he won since he had touched the right death note.
After Matsuda shoots Light, light crawls to Ryuk and grabs his leg, begging him to write Near's name down in his Death Note. Ryuk smiles, agreeing to write the name down. After Light taunts Near, Ryuk clarifies that the name he's writing down is his own. Light never runs away and dies on the stairs instead of taking his final breath in the warehouse, aware that Ryuk has done it.