Well, that isn't the full title, but it gets a bit of the point across. The main draw is something else, which I'll be talking about in the next paragraph. So, before we get into things, yes this already has a lot of fan-fiction written about it, I can't help that this was the setting my mind was stuck on. Please hold your anger until the end.
You already know that the MC is being reincarnated into this world full of Demons, Giants and various other races, that's not what I'm going to mainly be talking about. No, my main effort in writing this is the protagonist's chosen ability: The Strength Force. Think of it as being the superior version of Sunshine, not bound to a cycle of being strong then weak, as well as not emitting dangerous amounts of heat. This power will give the MC the ability to augment gravity and use geokinesis easily as well. I'll put a direct quote from the wikia: "The host comes out with the ability to manipulate their physiological semblance by either strengthening or weakening certain aspects of it. Essentially learning to change and alternate aspects of themselves by increasing/decreasing gravitomic inception. Making an avatar or anything they choose to affect as infinitely heavier, tougher, denser and/or muscularly more robust. Using it on oneself causes a sharp increase in size alongside muscular density in the chosen host. Making them bigger, stronger and next to invulnerable." Alright, everybody understand? If not, you should head to the DC fandom, it'll help you learn about the power.
Onto the topic of MC creation, I'm basically focused on one thing: Reincarnation. Now, where the protagonist will be born is something I've thought deeply about. I have a few choices: Either he is born as the twin brother of Escanor, or he is picked up by him and Merlin during the days of the Seven Deadly Sins. I'm leaning more towards the twin idea, mainly cause we can change a couple of things that happen to the Sin of Pride.
Okay, here's my thought: I don't actually think Sunshine causes a psychological change, I think Escanor takes on a more prideful personality to protect himself from the trauma the power gave him as a child. I think he has a form of Dissociative Identity Disorder. It's kind of like Bruce Banner and the Hulk, except more mild. So, if there's say, a twin brother that has similar abilities, he might not develop that overly confidant facade. I can definitely say that Escanor having a twin brother as the MC is my best idea for the character. I guess I can see how it might affect the storyline, since Escanor isn't prideful, he never becomes the Lion's Sin, but we can just have the MC take his place.
The whole "being picked up as a child by the main cast" has already been done by The Eighth Sin: The Sin of Love, so I'd like to avoid that similarity altogether. Granted, in that novel, he's picked up by Meliodas, not Escanor, but he's still trained and raised by the entire group. I mean you could have him be born to a normal family that take care of the MC until he's like 5, and then have a group of monsters or bandits wipe everyone but him out, though I still prefer the twin brother beginning.