So for a long time I figured that Reapers would be a better unit to make early than Marines since you can use them to harass...

Well... I've unleashed a monster.

Players have been doing a 7 rax Reaper rush for a while but it's not that effective because it can be countered with a rush or by sending units against the player.

This build is immune to that.

So basically here's how it goes.

1. Queue SCVs until you have up to 11 supply queued. As soon as your minerals hit 100 after you've queued all your SCVs, send that 8th SCV that's out to build a Barracks at your choke as if you're going to wall (because you are). You'll hit 150 minerals right when your SCV gets in position.

2. Use your next 100 minerals to build a refinery.

3. Use your next 100 minerals to build a supply depot to further block the choke.

4. As soon as the Refinery finishes send two additional SCVs to mine it.

5. As soon as the Barracks finishes upgrade your Command Center to an Orbital Command.

6. Immediately following this upgrade add a tech lab to your Barracks, further blocking the ramp.

7. As your first supply depot finishes, send this SCV to scout.

8. Once the tech lab finishes begin producing Reapers and rally point them to your opponent's base (use your SCV to narrow down what base they're in).

9. When the Orbital Command finishes continue building SCVs, using MULEs, and using 100 minerals to build a second supply depot to finish blocking your choke.

10. Start harassing with Reapers, when you hit 150 excess minerals start building two additional Barracks and return to a standard Terran Infantry build.

This strategy requires a lot of micro. Don't try it unless you're an expert with micro. But it will also make you pretty good with move-hold, move-hold, move-hold.

Also, if the opponent techs to Stalkers or Roaches or Marauders, don't cry. You want them to do this. Now you just forced them to tech while you're switching to MMM. More than likely they will panic and you have a very good chance of rocking their world with your first push.

Keep your Reapers alive as long as possible and use them for hit and runs. Force them to run their units around their base. There's a good chance they will make a mistake. I've ever had players accidentally A-click their own workers or blow up necessary buildings. It's pretty funny.