Kenji asks you to retrieve three briefcases around Staunton Island with protection payments. As it plays out, the Diablos steal one of them and you have to return to Portland to finish the job.
The first two packages are pretty uneventful. The second one will have a single Diablo gang member nearby to fire on you as you arrive (a taste of what's to come). Run them over and proceed to the next location where you'll be told that the final briefcase is in Hepburn Heights back across the bridge to Portland.
A large group waits for you near El Burro's phone. Armor is recommended and using a scoped weapon to clear them out from a distance works well, although with some luck you can take out a bunch of them with your car on arrival. They are heavily armed so be ready to abandon the vehicle quickly once it catches fire. If you're lucky, the explosion might even take out some of them.
After it's done, grab the final briefcase and return to the casino.