A fanfic centered around the Pokemon Lake Trio in the Hall of Origins might involve a young trainer's journey. The trainer, curious about the legends of the Lake Trio, embarks on a quest to find the Hall of Origins. Once there, they discover that Uxie's knowledge is not easily accessible, Mesprit's emotions are overwhelming, and Azelf's protection is hard to bypass. But through determination and respect for the Pokemon, the trainer gradually uncovers the secrets of the Hall and forms a special bond with the Lake Trio.
One idea could be a story where the Lake Trio's powers are being misused by an evil organization. A young trainer discovers this and teams up with the Lake Trio to stop them. For example, the organization might be trying to use Uxie's knowledge - granting power to create a super - weapon.
Well, in a fanfic, the Lake Trio could face a threat within the Hall of Origins. For example, an evil force might try to steal their powers. Uxie's knowledge could be used for wrongdoings if captured. Mesprit's emotions could be manipulated to cause chaos, and Azelf's protection could be weakened. The story could revolve around how the Lake Trio overcomes this threat with the help of a brave trainer or other Pokemon.
One possible plotline could be that the Lake Trio discovers a threat to the world that Arceus is either unaware of or is causing (unintentionally perhaps). So they have to battle Arceus to stop this threat. Another could be that a powerful villain manipulates the Lake Trio into believing that Arceus is a danger and they must fight it.
You can start by looking on fanfiction websites like FanFiction.net or Archive of Our Own. These platforms have a large collection of Pokemon fanfics, including those about the Lake Trio. Just use the search function and type in 'Pokemon Lake Trio' to get relevant results.
In a fanfic, it really depends on how the writer wants to portray it. If the writer wants to emphasize the unique abilities of the Lake Trio and perhaps give them some sort of combined power boost, they could potentially defeat Arceus. However, Arceus has the advantage of being a creator - like figure in the Pokemon world. It has the ability to create and shape the world, which gives it a very high level of power. So, generally speaking, Arceus is more likely to be the victor, but in the world of fanfiction, anything can happen.
One idea could be a story where the Lake Trio unites to stop an ancient evil that has been awakened in the Pokemon world. They could use their unique powers of willpower (Azelf), emotion (Mesprit), and knowledge (Uxie) to fight the darkness.
Incorporate a complex plot. Don't just have them going on a simple adventure. Maybe there's a mystery surrounding their origin that they need to solve while also dealing with an external threat. You could also include some unexpected twists, like one of the Lake Trio getting corrupted for a while.
In fanfics, the battle between the Pokemon Creation Trio (Dialga, Palkia, Giratina) and Arceus can be really intense. Usually, Arceus is seen as the god - like Pokemon, but the Creation Trio also has incredible powers. Dialga controls time, Palkia controls space and Giratina rules over the distortion world. Their clash might be about power struggle or some sort of cosmic balance. It really depends on how the fanfic author wants to portray it.
It could be about the adventures of the Regi trio in the Hall of Origins. Maybe it involves their backstories, their powers, and how they interact within that special place.