A lot of spoken lines in the novel are used in the show but, the most obvious difference is that Nukku and Mokku aren't in the novel. They're just there for comic relief really but overall, the novel seems slightly darker with extra detail that makes it more believable. For example (without ruining the story too much) the part where a certain character thought to herself that happiness doesn't last forever - It's definitely not something a child would be told so I guess why that scene wasn't in the show.
Don't read on even if you are following the show just now because it seems they've juggled a few parts around and what you read here, might become a spoiler in a yet-to-air episode!
Prologue 1, 2 / Episode 6
Volume one of the original "Beast Player Erin" novel basically picks up from episode six on the night when the prized frontline Kibas die and, it dives right into the nitty-gritty details of what the Toudah carers did and what the beasts are. It notes how the middle line Toudahs are referred to as "Doh (Body)" and back line ones as "O (Tail)". Erin's still ten years old and isn't permitted to even touch the Toudahs yet although she is fascinated with them - so much that she can spend the whole day watching them swimming about in their water holes.
Other than that, it's fairly much the same as what happened that episode although Soyon seems to be a little more vulgar than she is in the show using "omae" to refer to Erin instead of by her name. "Omae" is usually used by males informally. In fact, the show seems to be a bit inconsistent when Soyon talks. For the lines that are taken straight out of the novel, she says "omae" while the original lines she either uses her name or "anata" which is a more neutral way of referring to someone.
I think the changes in the Anime were for the good because spending time to build up the strong bond between the mother Soyon and her daughter Erin just gives Soyon's death that much more impact. Also, if they didn't let Soyon learn more about the Toudahs it would be kind of hard to believe how she was so suspicious about their deaths.
Prologue 3 / Episode 7
The novel seems a little more violent in terms of detail too. The investigator whipping the Chief's head and blood splattering, Soyon's bloodstained body with a deep cut along her stomach to lure the Toudahs and a rock tied to her legs. Also, Erin can't swim. Soyon swims over so that Erin could climb onto her back before being cut free. Erin doesn't receive a bracelet from her.
Obviously they had to tone it down in the family show and seemed to use red flower petals to symbolise the blood instead. They probably decided to let Erin swim to make her image more heroic for the kids. However, at the same time, she's given a bracelet to remind viewers how much her mother's death meant to her to show she still has a weakness that makes her a bit more believable instead of those invincible heroes.
On the whole, I think the Anime had a bigger impact on me for the reasons I mentioned above - padding out the storyline to show the strong relationship between the mother and daughter before breaking it. In the novel it feels a bit too early.
Prologue 4 / Episode 8
A "fairy beast" lets the People of the Fog know about Soyon's forbidden act, "Souja no Waza" before Asson returns to the People of the Mist to report. They believe it's the form their ancestors took and looks like a human with golden eyes but with two horns on its head and legs of a wild beast. We also hear from Soyon's 60 year old mother who seems to lead the elders there. Already it hints what the "great sin" is and how they don't want the Grand Duke to find out. They also reveal Soyon killed them knowing they were at their offspring season and the Tokuji Water is like poison to them at this time.
The Anime missed out the "fairy beast" and didn't go into much detail how Soyon broke their oath but, I guess episode 8 is about Erin meeting John. It's not until episode 32 it's revealed and even then it doesn't say how she killed the Kibas.
Chapter 1-1 / Episode 8
Erin is washed up on a grassy embankment. John thought she was dead and was already thinking about burying her until he finds she was still breathing. He doesn't seem as nice as he is in the show because he sighs after noticing Erin's green eyes, knowing he's just brought a heavy burden on himself but was still ready to take responsibility. After treating her wounds, he also says she was a lucky kid who he managed to pull back from the gates of the dead. He tries to make her cry off her sadness but Erin tries to hold it in thinking she'll forget her mother if she did. She had thought about borrowing some money from John and returning to Saju's home who Soyon entrusted her to but when she remembered how they all just watched her mother get killed, she decided not to.
The novel also goes into a little more detail about the geography of the East ruled by the Grand Duke which had plenty of water allowing them to have a good supply of rice while the Shinoh in the West, was rich in wheat so they have dried cakes mainly for meals.
The show very much removed the above and gave John a gas problem. Clearly it's to make it better for children to watch once again.
Chapter 1-3 / Episode 9
Erin remembers seeing her mother handing many large silver coins she had saved up over to Saju's family to take care of her. She learned one shouldn't expect help from others for nothing which was why partly why she begged John to let her work while staying.
Chapter 2-1 / Episode 11
After Erin finds the books, John decides to teach Erin how to read as well as how to make harps. During their trip into town, Erin learns "Bird of Dawn" The book also goes into a little more detail about poison such as when a human takes some, the stench from their mouth can tell what poison it was.
In the show, Erin doesn't know to make harps and had to go into town to fix one in episode 22.
Chapter 2-2 / Episode 12
Erin did some odd things such as touching the furry honey bees to see if their fur was hard and prickly like their needles. She also tried to sneak under Tocchi the male donkey to see if he could produce milk like the female mammals...
John who was over the age of fifty-five at this point had thought about spending his remaining days at the summer house but with Erin here now, he wanted to save more money in case the day came she would get married. He had already thought about sending her to the academy but he hesitated because she had the Ahryoh's blood in her.
Chapter 3-1 / Episode 16
Iyar's father wasn't a craftsman who made harps but a carpenter who specialised in cabinets. He died when a building he was helping with collapsed and when Iyar ran off to find a doctor, he avoided a horse cart which lead him to become a Ze Zan so that his mother could live a better life.
He hasn't met Erin yet. I guess the way the show changed was to give Iyar more character than simply being mentioned as a very talented Ze Zan at this point.
Chapter 3-2 / Episode 17
First appearance of the Shinoh, Grand Duke and the other high status characters. This goes into a fair bit of history about the Kingdom of Ryoza and mentions that "Hiraka" means "hell".
It explains how the kingdom was in chaos and when Jeh appeared, people thought of her as a god and begged for her help. Hearing their cries, she brought the people together and formed the Kingdom of Ryoza. However, by the fourth ruler someone named "Hajan" from a neighbouring country invaded.
The Shinoh at the time offered to surrender to avoid any unneccessary bloodshed but one of her ministers, "Yaman Hasaru" begged her to grant him the treasure, "Whistle of the Toudahs" so that he could suppress the enemy even though it was forbidden. As a result of wishing to protect the people, he won and was given the title as the first Grand Duke and also the rights to rule Hajan's former territory. The ties between the Shinoh Jeh and Grand Duke Hasaru were close but as generations passed, Hasaru's grandsons decided to build up their army of Toudahs and conquered their neighbours to expand their rule.
Ramashik who was one of the earlier Grand Dukes had wanted to become the ruler but, because of his little respect towards the Shinoh and he believed like many people in the kingdom that they were gods, he didn't try to expand their empire any further.
Eventually, the Shinoh didn't have her own army because her kingdom was under the protection of the Grand Duke. Furthermore, because her land was made mainly of mountains, her people's harvest were low whereas the Grand Duke's land were fertile. It was only time before she had to rely on some of their offerings.
As this divide grew, the name "Wajak" was born to refer to the followers of the Grand Duke who were stained in blood conquering other countries. The Saigamul were extremely displeased at this and began to take action in the shadows, hoping to overthrow the Shinoh and allow the Grand Duke to be the king. This lead to the details shown in episode 22.
The show spreads out the scenes with the Shinoh and rand Duke whereas here, it's all gathered together. Not sure if this was a good idea because the image the show's been building so far is very shallow.
The show doesn't really mention what "Hiraka" meant when Erin was having that dream in episode 27.
Chapter 4-1 / Episode 15
4 years have passed just like in the show and the scenario is almost the same except for a few points. When John is troubled, it's Erin who reminds him of Kazhalm where Ethal was working at.
John also already felt problems with his heart and when his son arrived, he thought of it as a sign from god.
Erin had already prepared herself for their separation. Since the day her mother Soyon died, it was her belief that happiness won't last forever and that there would always be change. That was why she always spoke in a polite manner towards John.
Chapter 4-2 / Episode 18
Ethal seems to be fairly much the only character that matches with her Anime counterpart.
Other than that just some minor differences in terms of settings. Ethal only agreed to let Erin join the school because three students were expelled for breaking the rules, not completely because of John.
Chapter 4-6 / Episodes 20 - 21
Once again, Tomura's character is slightly different. Yuyan is pretty much the same, being the one to break the news about Erin taking care of the King Beast. The difference in the novel is that instead of keeping a low profile, Tomura storms into the room and makes quite a scene. He accuses Erin of using her good relations to take Lilan from him and that it was because she was an Arhyou.
However, after Erin shows how much she wanted to help Lilan recover and hinted how she had once lost her mother too, Tomura calms down. Deep inside him, he was proud to be caring for Lilan but he was also afraid what was going to happen to him if Lilan was to die. After all, she wouldn't eat or drink any of the Special Water. He felt kind of bad about it but if Lilan was to die in the hands of Erin, at least he wouldn't be blamed.
He goes onto teaching Erin about how he has been looking after Lilan after she asks him to.
Chapter 4-7 / Episode 21
In the show, Erin refuses to use the whistle but in the book, she actually used it a few times while cleaning out Lilan's cage. However, she stopped after noticing how Lilan bit herself a lot whenever she woke up from the paralysis effects of the Soundless Whistle. Also, instead of singing and remembering Iyar playing the harp, Erin actually dreams of the wild King Beasts' cry one night and also John telling her how to play different sounds with the harp - Including the one that sounds like Lilan's cry.
And that ends volume one, leading into the next volume "King Beasts Arc".