It's Erika of Celadon City.
celadon city grass Pokemon
You have to defeat Erika.
The fifth Gym Leader in Pokemon LeafGreen is Koga, the leader of Fuschia City's Gym. He specializes in Poison-type Pokemon and hands out the Soul Badge.
The 8th gym leader is in Viridian City.
Viridian City, Giovanni(Team Rocket Leader) is the Gym leader.
Step on the portals until you get to the gym leader.
In Fuchisa city
beat the gym leader
Her name is Erika
Veridian city
On cinnibar island.
you get it at safron city gym leader