6(TTIRAAS)

An au where Mikami Satoru was best friends with Honjou Ryoma and helped him raise his son, Honjou Masayuki, after his wife died when Masayuki was 5.

Satoru dedicated his whole time to his job, friends and helping raise Masayuki which that being another reason why he was single and virgin(and also Ryoma was a very handsome man that when the two hang out, everyone was always looking at Ryoma instead of Satoru).

So when Satoru died, he asked Tamura to tell Ryoma and Masayuki that he loved them and to apologize for him leaving when he promised to be there for when Masayuki graduated college(yes, Satoru died when Masayuki was still in high school but it could be before or after he saw Velgrynd).

He is reincarnated as a slime, named by Veldora, etc but he basically treats most of his subordinates as he would Masayuki as despite them probably being older than him, they remind him a lot of the boy he saw as his son(so please do not make it a Rimuru x Milim or Rimuru x Chloe because this Rimuru would actually see them as children and not possible lovers...even  when they are adults...so Chloe would go that far to save her father figure and not her beloved)

Imagine Rimuru's surprise when he hears about a hero named Masayuki that is also a otherworlder so he decided to personally welcome him when he visits Tempest.

It was a complete surprise for Rimuru when he saw his Masayuki and he was worried about Ryoma as with Satoru dead and Masayuki there, he was left alone.

He approached Masayuki, talked with him for a bit but waited until there was only just the two and  said something only Satoru would know about Masayuki.

Masayuki would be in shock but wouldn't lose time in hugging his other father figure before spilling everything that has happened since Rimuru died(including how it affected Ryoma).

In my mind I was thinking that maybe Ryoma would die not long after Masayuki ended up in Tensura and reincarnate on someone(it could be a known character or not) and end up with Rimuru but I know some people don't feel comfortable in making Rimuru end up with a man(I mean, they could make Ryoma reincarnate in a woman and have him come to terms with it but it is their decision) but at the end it is up to the writer(or you could change that instead of Masayuki's father, it could be his mother...and the name doesn't need to be the one I used or a similar one)