Keep what you have. That's good, and that forms the basis of what you need for a workable plot.

When it comes to character development, what you want to do is add. Between each major plot event, take the time to write a scene or two with your character. Try to imagine him/her in between all of these events. Have the character talk to the other characters—show the audience what they really think and how they react "off the screen."

So, instead of "my character does this, then my character does this, and then my character does this," try to take your time with these things. What happens to your character after he/she accomplishes that first task? What is he/she thinking will happen next? How does he/she feel about what just happened?

All too often, I see stories that focus entirely on the plot. That's great an all, but remember, writing isn't about the destination. It's about the adventure and the experience of the journey. Instead of rushing to the top of the mountain to get that powerup, take the time to explore what happens before that. Imagine your character looking up at the base of the mountain, and imagine what they would be thinking if they were real. Are they nervous or anxious, or are they eagerly awating the next step to ascention? Are they worried about their loved ones? Are they worried that they won't succeed? Alternatively, does your character believe they're an unstoppable badass?

If anyone else is around, try writing a casual conversation between your character and the others. If you want to focus on plot elements, that's okay, but more importantly, just try to make it feel natural. When it gets quiet, is your character going to crack a joke? Does he/she want space, or want to be alone? Are they looking to have a friendly chat? Is he/she hungry? Is he/she sleepy? What does your character eat, and do they share? How do they react when another character teases them? What do they do for fun during the day?

If your character is all alone, try going inside their mind and writing their thoughts. Write about what they're doing when they're alone, and how they're reacting to this grand adventure. If they have a moment to, do they want to write a letter to someone? Does your character have a voice in their head that they talk to? Are they religious? What would he/she say in their prayers?

If you want realistic characters, you have to create realistic characters. Think of them not as bots who do what they're told to follow the script and make the story complete, but actual beings who are going through these events. Write out not just what's important to the plot, but also what's unimportant. Your character is a being who lives in this world you created—and if you're not expanding the world to show that, you're missing out on the most rewarding part of writing, in my experience.

Hopefully that should give you a few ideas. Characterization is one thing many of my readers have praised in my stories, so feel free to PM me if you need any more advice.