Re: aikido and competition
Check out my old posts as I have describe both tanto randori and toshu many times before.
But basically, toshu involves uke and tori coming and starting to do techniques on each other. It does not matter who attack first, just throw something and then when tori does a techniques react to it so it doesn't work and you are in a position to do a technique. Repeat till one of you manages to get a technique that works. The winning stage is not getting a technique working (it's boring and kata does that), it's making a technique flow from one to another.
Tanto randori involves testing your Aikido against someone who fully resists you with all his might and wants to club you one. Of course, it's done with a safety net -- at least in Shodokan. It's an exercise to see where you lack understanding of Aikido. Winning in tanto randori is having your favorite technique fail. It shows you what you have left to learn.
For all the years of Aikido I have done, I won every single match of toshu and randori because my goal is to understand Aikido.
Hope that helps.