It is a fender stay according to Honda AND is supposed to help the forks also.
.That is what is was told 15yrs ago when mine went missing on 88 Wing on the way to Florida the first time. I heard a noise up there and just thought i hit something.
Local trike dealer rebuilt my forks the first time not long after than and said it was missing. Uh OH moment. That was what that noise was. I didn't have a trike but they were supposed to be good but messed up stuff anyhow.
I didn't notice any difference in handling at the time, but it had to help stiffen the forks a little when it is installed.
i thought i paid $35 for a new one back then but memory could be off.