Comment by Ian Seamus on The One Within the Villainess - Chapter 23

There some bit after, such as showing Remilia had spent 15 years researching souls so that she can have Emi and the real Pina (not the fake bi***) be reborn as her and Angel's children.

Remilia had to start from scratch since Emi's memories contain no knowledge about souls let alone how to manipulate them. After years of research and experimentation on "rats" (rats in this case are what Remilia called her human guinea pigs, they were all ppl who wronged Emi, former classmates, disloyal servants etc) she would eventually with a little help from the Goddess of Purification contact the Spirit King who said he would help her with Emi's soul if she provided the original Pina a family that would make her happy in her rebirth. As for Angel yes she marries him in the end, bare in mind the way she behave in the story can be summed up as "Ah yes, this is how Emi's [Remilia] would act, this is what Emi's [Remilia] would do, etc" Remilia cares only about what Emi would want. She even monologues and I quote "Yes, I'm so happy. Angel loves my Emi's [Remilia] so much. I too could love Angel for loving Emi's [Remilia] so much." A happy ending with Angel is what Emi would want and Remilia made it happen.

Willard: due to his massive inferior complex, he went along with fake Pina plans to drag Remilia off her pedestal and humble her, obviously that didn't happen and he breaks down like a bi*** when Remilia kisses Angel at the ball realizing she's genuinely happy without him. His brother will replace him as crown prince. 
David: has a inferior complex towards his ex-fiance Sofia, when they were younger he hated how she was better, when they got older he hated how she was never bothered by him improving over her. He wanted a woman to "protect" ie fake Pina, he wanted to bring down Remilia so he could "protect" her, it's really stupid. Lives the rest of his life miserable to the fact he could never be a good knight who can keep their oath like Sofia could.
Stefan: couldn't acknowledge the fact he was lacking as a musician, knew that the whole situation with Pina was sus af yet chose to do nothing about it, wanted to be Remilia's "number one". In the end he lost his first love, first fan and best friend all at once and accepted he has no right to be sad about it.
Claude: was never effected by the charm potion in the first place, he wanted her disowned and isolated from the family so he could legally marry her. Didn't stutter he was in love with his own sister, but boohoo for him since their family fell into debt and his sister hates his guts.