If there is magic it could be very powerful if the protagonist can use it since if he uses the basic knowledge of science he could enhance it if he obtains elemental magic such as making the fire hotter by adding more oxygen or having almost infinite water by removing it from the atmosphere thanks to the particles that are hydrogen and oxygen

He will use graphene in his power armor that will increase its hardness and resistance against weapon attacks and enemy blows.

A good material that I could use would be graphene. It is a good material as hard as diamond and a good electrical conductor and energy storage. It would be good to use it and if it does not exist in the Marcel universe it would be good to discover it.

It would be good for him to learn the eight doors since it has a high healing factor, he could take advantage of it to make his body stronger by using that technique.

I'm curious about something and that is if it improves the body that you have possessed and that is that it could control growth hormones and make your body become stronger and more resistant thanks to improvements in your body.

then David in this universe will die from the virus that unexpected

out of curiosity it will only be a couple or harem

Do you know if you do the story of Naruto, the protagonist who is reincarnated would have more chakra than a common ninja, thanks to the yin chakra of his soul and he could make it one of Orochimaru's experiments, which would be the fusion of an Uchiha and Senju.

out of curiosity there will be a harem or a couple

You know, I'll be honest with you, I won't like Yang to be paired with Vegeta, give Bulma's sister the blonde, but not Yang, that could make me leave the story, and I'll be honest with you, I don't like Vegeta, and I want to see him suffer.

If there will be a harem since you can obtain DNA from other people's bloodlines, you could have a harem since the village would not have problems, thus having more stronger ninjas in the village

Aisha will then be born as his daughter and will not be his sister. It would be interesting to forget that now that she is stopped, she is already fertile and can get her women pregnant. It would be very good for the story.

Do you know something that the protagonist could do is give himself improvements to his body such as increasing the strength of his muscles and bones by controlling hormones and coating his bones with nano carbon something like the Spartans from Halo

Now that I realize I could have more chakra since the spiritual reminiscence could grow it more and not only that I could obtain more bloodlines in the future and with that I could gain more power and also obtain the elemental affinities making it more natural

You know, the protagonist could have a harem since if he can copy his Uchiha blood lineage and so on in his genetics, he could create a new clan and obtain more powerful nymphs in his line for the future.

You know, it would be interesting if women get pregnant, it could be that the pregnancy lasts less than a human and they have it in about 3 months instead of the 9 months of a human pregnancy, thus creating a clan of hollow wolves and conquering the hollow world.

Do you know instead of Guru dying he could fuse with Nail to make a super Namekian and make the Namekians have a better defender for future battles

Elicia would be the first to get pregnant and I think they will be thinking a little about the children after or during their honeymoon

You could do physical training and damage your muscles and bones and use medical ninjutsu to heal faster that will help you both physically and not only that but also in increasing your chakra reserves.

I see Bulma in Kron's harem as more possible than being with Vegeta and Raven, also because she would look for a strong partner and have strong children.