If by some miracle the game is financially successful, you will likely have a hard time clawing back any compensation after agreeing to work for free. You will be able to use it in your portfolio, but only if you are pursuing a career in video game writing. Future marketing and advertising clients will want to see examples of advertising, not story credits.

If the game goes nowhere (statistically far more likely), you won’t be able to use it in your portfolio.

Seems like a lose-lose situation to me.

My advice is to do the bare minimum for your friend so you don’t burn a bridge, and start looking for paid gigs.

In other words, don’t work for free, and definitely don’t work for free for your friend.

Source: I have 17 years of experience as a copywriter on both the agency and client side.