Bladebound Magus Roleplaying Advice

[Slayer Lord]

I'm trying something pretty new character-wise in our new campaign, and I'd like some tips on how to really shine with this character.

Normally I play paladins or clerics who are pretty straight good guys and the party peacekeepers. This time I'm doing a bladebound magus whose sentient sword is trying to push me towards the dark side. Even before finding the sword, my magus' homeland is being overrun by a plague of killer fungus (think "Nausicaa of the Valley of the Wind" or Vault 22 in Fallout New Vegas) so all of his time and energy is directed towards trying to find a cure even at the expense of others. He is True Neutral. Edit: Our DM has allowed the black blade to be one step away in alignment for story purposes

What I would like to do is strike a balance between dark and a bit self-centered without being an abrasive liability for the rest of the party. What are some ways you have played or interacted with antiheroes in past games?

[Geddy2112]

You are a magus, so you are int based-come off as the scientist/academic type that eschews morality and ethics for results. Those kind of debates are fun, and certainly you can see merit, but you have people to save and a cure to develop. You have a good heart, and maybe even a lawful bend in trying to cure a plague in your homeland. The sword is probably trying to convince you that through power, you can get that cure. That evil is the best and fastest way to get the results you want.

You are out for #1, but you see the value of a team working with you. You know there are skill sets you don't have that could be useful, and that you can gestalt(not the playstyle, but the meaning that the whole party is greater than the sum of the parts) through teamwork. Sure, you might be a bit more pessimistic or grizzled by the darkness of reality, but you are not a monster. You are no murderhobo- there is no killing for fun, or stealing for any personal glory, or engaging in reckless insanity. You might do some things that are morally or ethically wrong, but you do them for your goal. I doubt you will be a problem.

I am currently a similar style witch in a pathfinder campaign. I don't have a village to save, but I am trying to gain knowledge to solve a personal mystery. I understand the need and value of companions, and have even come to like them. I look at situations with cold logic, picking what to do based on what is the best outcome. Also, you could use a bit of Rick from Rick and Morty as inspiration, minus the overtly chaotic aspect.

[Ninjaxenomorph]

The wrinkle I see with wanting your black blade to 'push you towards the dark side', is that the black blade is always your alignment. It can't really want its bearer to be another alignment, since you will always share the same alignment. I mean, I could see a deluded evil black blade wanting it and its owner to be good, but it would never actually get there.