I should note that with most characters he will find either annoying or be easily annoyed with on regular or daily basis unless otherwise is specified.
Nex holds no personal opinion on Harold except for the fact that he is an excellent digger and can sense minerals which Nex likes to use to experiment. Nex makes sure he can stay on the good side with Harold in case he needs him to do a favor for him.
Nex has huge respect for Nicolaos. While he normally doesn't listen to what the others have to say, he takes Nicolaos commands very serious. The reason behind his respect for Nicolaos is because Nicolaos is the first person to speak to Nex like a normal human being. Most people either approach Nex with disgust, fear or pure hatred. Nicolaos didn't. A simple thing, people might say, but for Nex, this is the highest honor a person can do to Nex.
Darwin is a quiet man.Not that Nex has any problems with that. The only problem Nex has with Darwin is the fact how he doesn't want to kill anyone. He thinks he's naive for not allowing them the pleasure of dying, since being left alive in pain must be much worse than death. But other than that, he hardly has an opinion on Darwin, and maybe that is what makes it a much more dangerous relationship. People that Nex don't care about are people he see's as dead.
Lissa is one of those character Nex just likes. Maybe because she's female (and hot) but maybe because she too holds a dark past which she doesn't wanna talk about, something that Nex understands very well.. He also holds respect for her since she too has experienced the same thing as Nex, being looked with disgust by the general population. The only time Nex get's in good mood is when Lissa is teasing someone or when they become chatty.
Nex see's himself a little bit in Lissa, both due to her mysterious past but also because she has much raw power she has yet to be able to control.
Nex dislikes Setsuna alot. Most of it is because Setsuna looks for flaws in people (that Nex does too) but has no background reason for it (as far as Nex knows). Nex hates people because people usually hate him, for Setsuna to do the same without meeting the same disgust, annoys Nex alot.
Nex finds Ishman a bit curious. You might find Nex ask Ishman some simple questions about his skills and such. The reason being, Nex being knowledgeable with almost everything, holds little knowledge of Ki. Most Ki users aren't scholars or reaserchers and therefore, the studying and knowledge off Ki is somewhat little as close to nothing.
Nex always tries to experiment with or on Ishman with different things, so Nex can gain more understanding on Ki.
The first character Nex really hates. Mostly because Cathair seems to him to be all muscle, no brains. Forcing his way through things not to mention his pure arrogance really annoys Nex alot.
Everything about Cathair annoys Nex and most everythin Cathair might suggest or say, will make Nex grumble, even if his suggestions are good.
There is something about Jimmy that annoys Nex, maybe it's his arrogance, calling Nex old or asking Nex if he needs help and such. Although such things might make most people angry, Jimmy's retort are unusually witty as well as his comeback and as such, Nex always returns most of Jimmy's retort with sarcasm. He also likes to call Kage, Jimmy, mostly for it's sarcastic tone as well as to make sarcastic comments on his "age" compared to Nex. In most cases, Nex looks at Jimmy as a child but people generally find children to be funny, and this, sometimes, holds true with Nex's and Jimmy's relationship.
Most people don't have or know how to come up with witty remarks or sarcastic comebacks and for this, Nex... for some reason... holds a slight respect for Jimmy. Why that is is everyone's guess.
Nex also likes to compete with Jimmy in shadowy skills.
Nex doesn't really have an opinion on Acan. Acan respects other people's wishes and because Acan tries not to insult Nex, Nex returns the same respect. Because Acan leaves Nex alone, Nex returns with same respect.
Also, Nex loves each Acan's comment when Acan comments on how situations could be worse and also how Acan is calm in tough situations, just like Nex.
Estia's carefullness in battle, not to mention her intelligence and how she holds honor to someone higher than her (in intelligence) makes Nex respect her. This also holds true to how she honors what people say.
Estia likes challenges, something that she and Nex share a common interest. Nex doesn't like to challenge Estia but he likes how she makes something seem like challenges.
However, Nex always appears annoyed with Estia even though deep down he holds respect for her. This is mostly due to the fact that he can't overlook how she doesn't hold the same problem as Nex has with age. Estia can grow hundreds of years old and still seem young while Nex, whose age is forced upon him must suffer through all this. Nex is aware that his next century of life will be filled with anguish and pain. Because of this, Nex always distances himself from her, knowing the closer he gets to her, the more annoyed he will become.
This is the main reason why Nex might seem to hate her, even though he would wish for nothing more to teach her everything he knows. But he can't overlook this blessing she has.
Nex thinks of Maria as a useless person. While the truth might be far from it, Maria can't help Nex with his ailment and for this, the fact that she calls herself healer, while not being able to heal his pain, makes Nex think of her as a useless person.
Deep down, Nex feels disgusted with Maria, feeling that she is useless, he feels she is compensating her "uselessness" with "caring" and "love". This fact however, Nex tries to hide desperately because she is the only one who can really scold the others and he doesn't want to lose that opportunity to use her for such things.
If there is one thing Nex can't resist, it's occult magic, or in this case, Aidan holy symbols that he draws on himself. It's divine protection was somewhat of new to Nex. Ofcourse Nex knows he can easily outmagic the protection but he will come out badly in that combat and Nex knows that.
However he really hates Aidan arrogance, of thinking about Nex as some old guy and that he should "know his place" as Aidan put it one day. He really doesn't like to show Aidan his skills, as he feels his hatred to him will only grow worse. For this matter, he always distance himself with Aidan and tries to go in group with someone else when the group splits.