The MC dies and gets his wish granted to be 'like' his favourite character, Lion El'Johnson. What he didn't specify, is where he wants to be born. Thankfully, the ROB who reincarnated him gave him something on the way in the form of a Meta Essence. This should allow him to become the strongest of all Primarchs, no question. In this story, the MC won't go back to Warhammer 40k. That will happen in another one after this one is finished.
Essence of Evolution
Drinking this imbues you with the power of the ever-evolving ultimate life form.
- Adaptive evolution Counter (What doesn't kill you makes you stronger) You're body will adapt and evolve, whether from extreme environments or getting cut by something sharp, your body will make its counter.
- Adaptive evolution Death (What does kill you makes you stronger)If something manages to get past your counter and "kill" you, you will become immune to whatever killed you.
- Adaptive evolution Consumption (It tastes like chicken they say) Eating something will allow you to store or gain their traits for your evolution.
- Adaptive evolution Guided (Sometimes you need to take fate by your own hands) It would take longer but you can enter a state of change where you guide what evolution you want to take place without being exposed to danger or killed.