1(TTIRAAS)

Satoru wasn't Rimuru's first life, he had been first born as a high human in Tensura but died and reincarnated without memories as Satoru and when he reincarnated back in Tensura he only had his memories as Satoru.

As he and Great Sage evolved, Rimuru had dreams about his past life but when he woke up he couldn't remember them. No matter how hard he tried to remember them, he could only remember the emotions he felt in his dreams but nothing else and while most of them gave him happy feelings there were some that gave him an immense feelings of pain that when Great Sage compared to something in the world it translated to period pain or giving birth.

The dreams continued until the he fought and won against both Velgrynd and Veldora, that night for the first time he dreamed of his first life and remembered it when he woke up.

Rimuru had once been Lucia Nasca, wife to Star King Veldanava, mother to Milim Nava and sister to Rudra Nam Ul Nasca.

He had been pretty confused and he needed some time to came to terms with what he had just found out especially as his self-claimed best friend was his child in his first life.

But maybe it helped that now that Rimuru had his memories as Lucia, that he could sense Veldanava's soul in Ciel meaning that the true dragon has chosen to reincarnate with him.

How it would go from here, I am not sure but the idea comes from that true dragons can be reborn but Veldanava didn't seem to have been reborn like his siblings so it made me think what if he wanted to be reborn/reincarnate when Lucia's soul did? He separated most of his powers from his soul(still leaving a small part of his soul and conscience behind with his powers so it wouldn't go on a rampage) which he tied to Lucia's soul and waited until she reincarnated again in Tensura which made me think that Satoru/Rimuru was the best fit for her reincarnation especially with how powerful Great Sage/Raphael/Ciel was and how he evolved so fast with their help.

So, yeah...it probably makes no sense but it was one idea that didn't want to leave my mind especially with me having seen a few fics or videos mentioning Rimuru being Veldanava's reincarnation or how similar the two are, so why couldn't he actually be someone else's reincarnation like Lucia.