One of the first things I do when it comes to breathing life into my characters is to write down a short overview of their personalities using contrasting and/or conflicting descriptors. "Character is This but also That. Does X but is also Y." I find it's a nice starting point in making them realistically complex, and also diverse – having Character A be "X but Y" and Character B be "X but Z" can be a good way of establishing what kind of dynamic Characters A and B have or would have.
"CLARE – Assertive, confident, but sometimes too eager to put her abilities into use. Shrewd, more observant than she lets on, but sometimes jumps in before knowing all the details. Quick-witted and has a good heart, but unconsciously thinks of herself as being a bit invincible."
One of the basic storytelling principles boils down to "Someone wants something badly, but is having a hard time trying to get it". This is pretty much the same idea, just with different wording – "Character wants X but is opposed by Y. Needs to do Z, which they may not want to/be equipped to do". I use it to get an idea of what sort of obstacles I might throw at my character during the story's events and the arc they'll undergo – it doesn't tell me what the obstacle will be exactly or how the character will deal with it, but it's a fun place to start and a good reminder/reference point to come back to if I get stuck.
"LINUS – Wants to protect his friends and his city, but lacks the self-sufficiency and experience to oppose his enemies on his own. Needs to overcome his naïvety and self-doubt and learn to take the initiative in a tight situation."
This is one of my personal favourites and also helps me determine how a character might move, be it in a fight or making their way through a crowd. Since No More Heroes is fairly action-heavy (following in the footsteps of the visual media I love so much) this is a pretty key aspect to my planning stages – I use this as a way to plan in advance how my action/fight scenes might play out, but it could prove useful to you as well, depending on what you're writing (conflict doesn't have to be literal, after all). There are three parts to this technique:
A. Fight, flight, or freeze?
B. First strike, or wait it out?
C. Offence vs Offence, Defence, or Deflection?
"MALLORY – Prone to freeze; will wait for their opponent to make the first strike before moving. Combats Offence with Deflection, using their opponent's strength against them."
Thanks for reading!