The invasion is nothing personal or for revenge. Kilorita did steal the child of the plane from Legion-7, but that's not the reason why they will be invaded. Legion-7 hid a lot of the wealth he took from the dead gods in the plane. Someone has to go and get it. Plus there's more wealth that the Celestials are hoarding. So the invasion is strictly business.
It may have a side of pleasure but what was strictly business was when the tree father made a demigod of order and killed the girl for her core so that Legion-5 could acquire the divine ability of Order. It was also business when Legion-5 killed several great gods to enhance that divine core to the level of a great god.
Many people have sacrificed a lot for Legion-5's plan including the clones of the Legion. Aeternus even gave him one of his crowns and helped him get a Celestial godhood of order. This is just to see if his plan will work. If it works then he will need even more investment.
One of the major investments he might need for his project is a world seed. This is all because Legion-5 believes that the combination of Legion-7, who is a living Authority on par with a Supreme law, with an inner world, the Godhood of a Celestial, the Authority of the Celestial Supreme, and the crown of a demon king will lead to something great.
Legion-7 has a spark of consciousness which represents the apex of spiritual Authority. The godhood of a Celestial represents the apex of divine Authority while the crown of a demon king represents the apex of sin Authority. All of these will be fused on a foundation of the law of order which is the divine ability of giants of order. Then it will be enhanced by the Authority of the Celestial Supreme.
Legion-5 has been preparing for this combination for a while now. Many great gods have died so that he can use their godhoods to perform experiments. The remaining godhoods that he didn't use were given to Aeternus to make up for the Celestial godhood that he would need. But the Authority of the Celestial Supreme is unpaid for and has already caused a deficit in their wealth.
Fortunately, Legion-5 is ready for the fusion now. Still, he did some final preparations. At this point, their understanding of the laws and the world has reached a level that most Origin gods cannot compare with. It is because of their understanding of the world that Legion-5 thinks his plan will work.
They know that a world is made up of a world spark, a world engine, and a world seed. So if he is to become a world god without a supreme law, he is going to need all these things or things that will substitute for them.
Legion-5 himself intends to become the world engine. He has a dragon heart that is the apex of the path of perfection. This heart is capable of refining normal spiritual energy into dragon force. This dragon force can replace the soul force of origin gods to refine void energy into Origin essence.
They have already seen in the situation of Legion-8 that if the soul force of an Origin god is used to create dragon force, then cosmic energy can be utilized to a certain extent.
While Legion-8 can only use cosmic energy to strengthen his inner world, they have gone further than that because Legion-7 combined with Legion-5's inner world. Legion-7's partial manipulation of cosmic energy plus the dragon heart's potential for the manipulation of cosmic energy should ensure the success of becoming a world engine.
This is in an attempt to create a small low-powered world engine capable of growth but it is only part of the equation. The result of the fusion of Legion-7 and his inner world will be empowered by the fusion of the Celestial godhood and the divine ability of giants of order. Then it will be balanced by the crown of Chaos.
This second part of the fusion is to elevate the substitute world engine into something powerful enough to carry a world. It is only then can he fuse with a world spark and world seed to become a world god without a Supreme law.
To create the effect of a world spark, he intends to fuse the Authority of the Celestial Supreme with his substitute world engine and use the product of the fusion to advance to the Origin god level.
So whatever he creates will be his concept and should substitute for the need for a world spark just as the concept of a realm lord substitutes for the world spark in a world heart. It is a daring plan that aims to achieve qualitative power through the advancement of the product of quantitative fusion.
That will surely make it into a world spark and if his substitute world spark doesn't work either, Legion-7 will fill in it for it when they become an Origin god.
He is confident that his plan will work because Legion-7 is already the equivalent of a world spark. He grew from the level of a living Authority to a living world spark after refining the Supreme law of the Serpentine world god. All that will be left his plan works is the world seed.
Legion-5 finished reviewing the plan and checking to make sure everything was alright. Then he said, "Let us begin."
His dragon heart has fused with Legion-7. His giant of order divine ability has also fused with it. The divine ability of giants of order awakened a third ability when it was upgraded with the godhood of all the great gods that he has killed over the years.
As it is, it has broken through the limit of great gods and sovereigns. But it won't be able to awaken further without a supreme law. That is enough for what he wants to do.