Early Days
When Billy was Seven years old, he met Kusunoki as a little Aron, and was given the young Pokémon as a Lesson in responsibility. As such Billy would feed the Rock and Steel type, pet it, play with the Pokémon, and even do some light training with his father, Elliot's help. As such, the two became nearly inseparable by the time Billy was Ten. On his tenth birthday, Kusunoki was officially handed over to Billy and he went to see professor Birch to pick up a starter, he had Kusunoki help the decision making of selecting the Starter by interacting with the Starter Pokémon. Torchic tried to scratch Kusunoki, whereas Treecko attacked immediately, but Mudkip was friendly compared to the other two, Which told Billy that Mudkip would be best for his Starter. He was given a pokedex, Mudkip's pokeball and a idea to face Roxanne in Rustboro City.
Keystone Acquisition, The Underground Ruins Exploration.
When he was Fifteen, he had heard of Geosenge town, going there after a harrowing ordeal of a battle versus his Cousin's traveling Companion Maximus. He was looking for some way to bring his bond with Kusunoki into play, and had stumbled onto Mega Evolution as a possible way to use the bond he forged with his Aggron. He had heard about a set of Ruins that may have had a Keystone. As he went through the region, he had discovered the set of Ruins, and upon Entering the ruins, Kusunoki popped out of the Pokéball, immediately looking around when a stray Flash Cannon went past a pillar and towards Billy, Kusunoki acted to defend his trainer with his life if the Pokémon deemed necessary. A Lucario walked out and gave Kusunoki an issue of challenge. Kusunoki went blow for blow for a while as Billy gave the commands. Billy was on the verge of tears and placed himself in between Kusunoki and the Lucario as the Lucario went to end Kusunoki when something strange happened, he bursted pieces of metal at the Lucario, sending it flying Away from Billy. Billy looked to see the Lucario in the wall, and Kusunoki looking at the Lucario with an unhappy glare, as if Lucario tried to attack someone precious to him. Billy had realized that their bond gave the moment of need which had triggered mastery of Metal Burst. Billy and Kusunoki went further into the Ruins, as Lucario guided them to the final chamber, where the Keystone was held. It was up to them, and their bond to find the Keystone in that chamber, they trusted each other as they separated to try and cover more ground, but it had proven fruitless. The two met back at the middle, and worked a different strategy, sweeping the place together, but Kusunoki taking high and Billy taking low. As the two searched the chamber, the chamber had something else living in it, an Alolan Golem. Billy had figured someone released it, or left it to guard the Keystone's location. The two, were ready for anything. The Golem immediately earthquaked, which activated Aggron's sturdy. Kusunoki had a part of an idea that Billy finished. Billy had Kusunoki go and Metal Burst the Golem. The Golem was not amused as it Went for a Thunder Punch. Kusunoki had a similar instinctual plan to what Billy was actually planning to do, and naturally Dragon Rushed past it. Billy knew he needed to trust what Kusunoki was doing, as the same applied in vice versa. It was when Billy was nearly caught up in a Thunderbolt from Alolan Golem that Kusunoki managed the KO, his trainer was a bit Paralyzed but he knew that his trainer would make it. In account for his Trainer's paralysis, they slowed down a but as the two worked together in Reverse of the second search, as Billy rode on Kusunoki's back. Billy and Kusunoki eventually found the Keystone above where they fought Alolan Golem. Billy was sitting on Kusunoki's head, as Kusunoki somehow knew where to place Billy as to not hurt him. When Billy grabbed the Keystone, Kusunoki had Let Billy down and the two walked back the way they came through the final chamber, Billy leaning into his Pokémon. The two got through the chambers of this underground Ruins, and sat down when they got to the Pokémon Center. Billy looked at the Keystone. He looked at Kusunoki and they both knew they had something else to work on.
Mega Stone Acquisition- Trial Of Metal and Mental.
It was Shortly after his Sixteenth birthday when he was back home again in Hoenn when he got a letter about Mega Stones discovered in Meteor Falls. He immediately got Kusunoki and his team to trek into Meteor Falls. He was able to get into the falls and start his search. Kusunoki had to trust Billy in some parts as they were too small for an Aggron. As Billy looked around, he wasn't finding much. At first he found a wrong Stone, but it wouldn't work. He kept the false Stone in case he needed it to do something. They searched cave after cave. It was after getting into some of the deeper sections he noticed a door, and being the person he is, Opened it with Kusunoki. The two walked into the room and immediately prepared for Battle. A Mawile had stood in their way and challenged them. Billy and Kusunoki won that one rather quickly, thanks to their trust in each other. They beat three other Pokémon, each more difficult than the last, until the fifth and final Pokémon, a Metagross. Kusunoki prepared as well as Billy, and the two fought what could have been the final battle of their lives. The Metagross had been playing mind games with the two, trying to turn the two against them, but every time, they were able to reiterate themselves to trust what the other was thinking. Kusunoki looked at Billy as Metagross went to Hammer Arm the trainer. Billy knew this was probably his end but Kusunoki had taken the attack meant for his trainer, the Aggron had three Metal spikes stuck in its left leg as he knew he had to finish this, and with Billy's help. At that point, the Mega Stone, Aggronite, had been lodged into Kusunoki's left Leg by Metagross. Billy hoped the bond was enough, as he thought of words that represented their bond.
"Though the trials of Life and Battle are tough. Even when we face the End, we must Soldier on, Kusunoki, Mega Evolve!"
Billy had made the Key Stone one of the collar buttons on his shirt and the tendrils of energy went between Billy and Kusunoki. At that point the Mega Evolution Sphere appeared around Kusunoki, when it broke, the DNA symbol meaning that he had successfully Mega Evolved into Mega Aggron. Billy held his hope strong and knew their bond was stronger than his hope. At that Point, Metagross went for a Hammer Arm, which didn't do as much as he thought it did. He then ordered Kusunoki to use Iron Head, he used Iron Head on Metagross, but proceeded to restore some damages to the cave they were fighting in afterwards. It then wore off unexpectedly. Billy realized Kusunoki's condition at that point and knew both him and his Pokémon had to make the right moves to get out of this.
"Let Metagross Hit you!"
Kusunoki was confused at first, but listened to his trainer, signifying his trust in Billy, his trainer. The Metagross hit Kusunoki.
"Finish this, Metal Burst!"
Kusunoki used the Metal Burst as if this Metagross had encroached on his territory, and his territory was anywhere his trainer was. Metagross fell over knocked out. The Aggron looked at his trainer and fell over as well the toll of fighting five Pokémon had hit the Pokémon, Billy returned Kusunoki, and got out of there, going the way he came and he got out of the falls and went to Fallarbor town to See Nurse Joy. He explained how he came from Meteor Falls and needed his Aggron looked at, he was beyond worry, and sat, waiting. He didn't sleep until he heard his Aggron was okay.
"Your Aggron is exhausted, what did you do?"
"I found an Aggronite, which was guarded by Five Steel types, fought in increasing difficulty with the last being a Metagross, that was a tough fight."
"There is an Aggronite lodged in its left leg and we can remove if you want."
"Don't worry about it."