@Uncle Buck The first question will be a Yes and No, a yes because he did say there was a connection between the three energies (shadow energy, magic energy, and sword energy) but I haven't read it happening and a No because he can't connect the lighting energy with the other three energies because that is a different type of technique altogether that is why he users a different sword when using that technique.
No he can't summon Solderet because he is a G** and the contracts were made so that if even the g** wanted to descend into the world they would have a human body to descend in and Jin using Solderet's shadow energy was just a byproduct of that contract, it is because Solderet has chosen contractors before that is why the shadow energy itself has been turned to different types of forms and techniques over time. Even now, Jin is looking for a way to talk to Solderet because he has not spoken to him since he was young.
No he can't summon Solderet because he is a G** and the contracts were made so that if even the g** wanted to descend into the world they would have a human body to descend in and Jin using Solderet's shadow energy was just a byproduct of that contract, it is because Solderet has chosen contractors before that is why the shadow energy itself has been turned to different types of forms and techniques over time. Even now, Jin is looking for a way to talk to Solderet because he has not spoken to him since he was young.