Stealing Heroine: Honestly, I never thought this far. (Warning Mature)

[ Beware this fanfic - made by google translate from Bahasa to English and some little editing by free website ]
Suzuki Kouta got an unknown illness and felt like dying, at that moment he could remember someone's memories. Someone who succumbed to illness and died at his age. Someone who came from another world that didn’t look like his world at all.
The problem was those memories felt really real. He could feel every emotion those memories felt.
What are these memories?
Is this his past life memories?
Transmigration?
Reincarnation?
Or two souls were merging?
Who he was right now? His previous life or Suzuki Kouta himself.
Where does the soul come from and where does it return?
He didn’t know why he got those memories, but he will use these memories to the fullest and didn’t regret anything.
But what is he doing with this new experience? Of course, enjoying life. But it looked like he got other things too…