Out of spite. This tale stars, like so many stories do, with a whining Toplaner. They spent the entire game complaining about needing help, so when I had nothing better to do, I decided to roam toplane (I was maining Leona support at that time) I decided to gank top literally just to shut our Toplaner up for a minute.
However unbeknownst to me, I had just made a crucial mistake. You see, I ended up doing the "worst" thing a support can do: My Aftershock explosion took the kill.
Naturally the Toplaner started flaming me, and even went as far as buying a support item and telling me to go play Toplane then, if I need the gold that bad.
This is however not the end of this tale, for you see, a person on discord saw my match-history and was curious about Leona without a support-item. So I explained that I was Leona Top that game and they went of on a rant about how Leona anywhere but support is garbage and I am garbage for even attempting it.
Now you can call me terrible at this game and you would be correct. I am very bad at LoL. I will accept you flaming me all you want because you are factually correct. However I draw the line at someone calling my main terrible.
So the game was on. I had no choice. I needed to climb higher than they were, playing mostly Leona top, literally just to spite them. I have technically suceeded in that, by climbing as high as Bronze I, however now I keep playing it to see how high I can go.

It's pretty much like a Leona support, except you have a lot more gold and a more steady source of income.
You can be tankier than any Leona support has ever been while also having the benefit of not being flamed by any ADC

Most people will only know Leona as a support, where she is not a champion before level 2. In toplane against Melee champions however Leona has a REALLY strong Level 1.
If you are against a Melee champion start Level 1 by doing a quick AA-Q-AA trade and ideally backing off while the enemy champion is still stunned, giving them no way of retalitation. If they insist on fighting it out, drag them into your wave and let them tank minions, this will either make them back off or give you a free first blood.
In general keep looking for quick tardes off Q and PTA/Electrocute CD during early laning phase

One thing that is consistent with Leona Support and Leona Toplane is the level 2 powerspike followed by the Leona lv 2 all-in
If you sucessfully lv1-cheesed the enemy toplaner, they should be quite chunked out and therefore unable to contest the wave, giving you a free level 2 advantage. Now they either respect it and backed off, or they will be hit by your E and die do your AA-Q-AA-combo.

Now your lane opponent either has TP or Ignite most likely. If they have TP, you won't be level 3 by the time they get here, but they will most likely not have gotten enough cs to get an item advantage, meaning you can just use the fact that you're level 2 and they're level 1 to send them back to base again. If they have ginite, it will be even easier because you will be level 3 by the time they get back to lane. After than push waves, look for roams mid, set up ganks for your jungler and do whatever you can do to spread your lead to other players. If you have a carry jungler, tell them to spam ganks top, you have SUPER good gank-setup, make use of that.