This is the perfect time to cast.
|— Natsuki Usami||”|
|Age||17 (beginning of series), 18 (later half), 19 (post-series)|
|Weight||57kg (125 lb)|
|Family|| Usami Tamotsu (father)|
Usami Sakura (sister)
Usami Shinobu (mother, deceased)
Usami Mariko (stepmother)
|Animation Debut||Episode 1|
|JP Voice Actor||Koki Uchiyama|
|English Voice Actor||Corey Hartzog|
A distant, cold, and quiet young man, he is silently judgemental and hard to get close to due to his mother's passing two years prior to the anime's beginning. Having been interested in fishing ever since he was young, he quickly gained fame locally as the "fishing prince", and his knowledge in the field causes him to unwillingly befriend a boy seemingly filled with rage, an alien, and an alien hunter.
As a high school student, Natsuki has a generally regular appearance. He has wild, out of control hair, that fans have described as his "asianfro" — his hair is later cut off by the other main characters in a fishing game, leaving it neater and shorter. He adorns black, thick, rectangular glasses, and usually small, curved eyes. Natsuki typically wears a serious expression, and he is rarely seen smiling.
Like the other attendants of Higarashi High School, he wears the typical uniform with nothing too special or unique — a blue blazer, black pants, black tie, and white dress shirt. Instead of the regular shoes, he wears brown shoes instead, and has a watch on his left wrist.
As other types of clothing, he is seen wearing jerseys and usually more plain, darker colors.
Natsuki is generally describes as serious, quiet, and hard to impress, as he is usually judgmental or uninterested in others fairly quickly. Because of his special talent and skill in fishing, he is nationally ranked as a "Fishing Prince", although, he does not like being called such. It is shown that this fact is not locally known, as other students of the school seem surprised when Haru greets him as "Prince", and only people like Misaki and Ayumi are aware of this fact.
Natsuki has little patience for others, not wishing to waste time or repeat himself when it is unnecessary. He generally takes things that mean very much to him to heart, and is passionate about whatever he loves, seeing that he repeats whatever goals he has (e.g. fishing, running, etc.) Despite his initially cold exterior, Natsuki actually possesses a king, understanding heart, especially when it comes to people he dearly cares about. He does not easily forgive and is shown to be somewhat passive-aggressive about whatever grudges he has.
Generally he seems to be uninterested in interacting with others, however, he does enjoy his bouts of fun, as he participates in fishing games, and does know how to do the Enoshima dance. When he is with his little sister, Sakura, his attitude changes and he becomes much more kind and welcoming, expressing his soft spot for her.
As a local of Enoshima, he understands many of the areas and seems to get around with ease.
Natsuki is a native to Enoshima, having lived there for his entire life. He was born to his birth mother and father, and it is implied his childhood was happy whilst his mother was still alive.
Two years prior to the series beginning, when she was 15, Natsuki's mother, Shinobu, had passed away due to unknown reasons. Due to this, Natsuki entered a stage in which he became relatively cut off and quiet, and the fact that his father began to date another woman did not help. During these two years and onwards, Natsuki became more and more hateful towards his father, not wishing to make a good relationship with him or improve it.
Natsuki himself began to take an interest in fishing when he was three, but did not start fishing until he was thirteen. 
Yuki is Natsuki's classmate and later a good friend. At first, their relationship is rocky as Natsuki always felt annoyed and frustrated with the other teen but eventually they grow to understand one and another, and become good friends. Natsuki is one who taught Yuki and Haru to fish, he even was the one who pushed Yuki learn howto set up his own rode to show Natsuki he wrong about his 'character'.
Natsuki is Sakura's older brother and only sibling. As siblings, the two share a very close relation with each other, as Natsuki has a weak spot for his younger sibling. Due to the fact they are the only other person that can understand the situation and pain of losing their specific birth mother, Natsuki and Sakura are shown to rely on each other deeply, as Natsuki is constantly worrying over his little sister. Sakura, in turn, always wishes to do whatever will make her older brother happy.
In Episode 7, Sakura and Natsuki have an argument which leads Natsuki to slapping Sakura harshly enough to leave a mark upon her cheek. She begins to burst out crying, and Natsuki feels no remorse initially over this actio, until near the end of the episode, Sakura disappears. A search party is created, and Natsuki ends up finding her in a closed off amusement park which he, Sakura, and their past mother used to visit.
Natsuki and Sakura quickly make up after the ordeal, and Natsuki, for Sakura's sake, agrees to start getting along with his father again and begin to express his inner turmoil over his mother's death with her more.
Otherwise, the two share a very well-established sibling relationship. Natsuki regularly cooks for Sakura, as well as sweets. He's really into making them fish shaped. 
Tamotsu is Natsuki's birth father. From the beginning, the two share a particularly standoffish relationship despite Tamotsu's desire to get along with his son. Natsuki, still upset over his mother's passing, distances and cuts himself off from Tamotsu whenever possible, as he is still angry that he had moved on to another woman in such a short span of time. It is shown that this is the main reason he resents his father, and thus, they do not get along very well. Haru had attempted to fix their relationship by mind-controlling them to fish together, however, Natsuki had quickly ran off, not wishing to spend any personal time with him.
In Episode 7, Tamotsu reveals that he wishes to turn the cafe into something else in order to fund the family, however, this angers Natsuki, and the two enter an argument that Sakura becomes involved in. Natsuki slaps Sakura, and the Natsuki's birthday party officially dies. The two make up sometime after this, however.
It is shown that they probably had a good relationship prior to his mother's death, as Tamotsu was the one that had created Natsuki's infamous "Eno-shima-don" saying. Tamotsu was also the one that Natsuki inherited his "I'll only say this once" phrase.
Shinobu is Natsuki's birth mother. From what the anime had offered, Shinobu and Natsuki's relationship as mother and daughter was good while she was alive, as they went to amusement parks together and shared fond memories. According to the anime, Natsuki loved and still loves his mother to a great extent, as he is seen praying at the shrine of her at his home, and offering foods to her as well in Heaven. At the beginning of the series, he is still troubled by her death and is unready to move on from her passing, especially since his father had began seeing a new woman. However, after an argument with Sakura, Natsuki was able to move on fully from his inner sadness and accept the fact that people must move forward.
Mariko is Natsuki's eventual stepmother. It is unknown how Natsuki feels personally about her, however, it is shown that he does not like the idea of his father "moving on" from his birth mother to Mari. If anything, Natsuki avoids interaction with her and does not desire to speak or get close to her, probably in fear that he, too, will "forget" about his first mother.
Erika is one of Natsuki's relatives, however, it is unknown what sort of relatives they are (most likely cousins, or some form of it). They are not seen interacting too much, however, it is confirmed they share a good relationship, as they give each other gifts during family gatherings, etc. 
- The '夏' (Natsu) in 'Natsuki' means Summer.
- Chapter 4 of the Tsuritama novel confirms he is 7 years older than Sakura, who is 10 at that point of the novel. This would mean he was 17 at the start of the series (the same age as Yuki) and 18 after he celebrates his birthday during the series.
- His birthday was later revealed through official art (2013, one year after the series ended) to be August 28th. In the same official art, he was shown to be celebrating (again) now with his whole family, including the new baby. This would mean he's celebrated his birthday twice since the series began, and thus aged two years since the series began (Natsuki would be 19 by that point). It should be noted the official twitter and merchandise also tends to recognize and celebrate all of the main characters' birthdays ever since the series ended in 2012.
- Because his birthday occurs not long after the Japanese school year begins (April), he is one of the first of the class to celebrate his birthday and age even at the start of the series. This also occurs before the major later half and plot of the story happens, and before he begins to interact more seriously with Akira, particularly, who before that was mainly spying on them from afar or otherwise acting distant.
- He is left-handed.
- Aside from fishing, he regularly goes running. He also enjoys playing classical Japanese chess. 
- He never stops his running hobby, even at the end of the series. 
- Natsuki's favorite music is grunge rock. 
- He prefers Pearl Jam over Nirvana. 
- Natsuki is good at math, and is bad at ball games. He claims it is due to the fact he cannot "sync" with others. 
- Fishing is the most important thing to Natsuki. 
- He takes pleasure in simple clothes, and dislikes anything that is tight around the neck. As seen in the anime, he has quite a few jerseys, but has never bothered to count. 
- Natsuki likes to cook a meal called "Big Brother Curry", which Sakura had named. It includes tomato, yogurt, and cheese. 
- Natsuki enjoys sweets and chocolates, and does not like shirashu (though, he had eaten it a lot in the past). 
- "Think the fish gave you time to think when you can't catch one." by Ernest Hemingway is a quote that Natsuki particularly likes. Misaki had taught him this. 
- His eyesight issue is most likely hereditary. 
- Natsuki dislikes smartphones or any similar technology. 
- Amongst the staff, Natsuki is the most popular character, at least with the girls. 
- Natsuki takes baths multiple times during the day, due to his running hobby. 
- His blood type is A.
- Blood type A people, in Japanese culture, are said to be gentle, creative, and sensitive.