Fullpower

kono hito denashi!

There are honestly a lot of loopholes he could use. For, example, the simplest would be to wish for immortality to his system. Or, he could make a department in his kingdom explicitly to the research of immortality and he could give them some clues with his modern knowledge. I mean, we are already using technology to increase the lifespan of certain dogs. In case the research takes too much time, he could request the future knowledge that the institute or department is going to get or use cryogenic sleep on fern until the medicine is ready. Alternatively, he could make fern into a demon using magic. After all, he already has a precedent in himself

He should be able to use "Golden Rule", "Wisdom of Dún Scáith" and his other skills to make a better kingdom, right? I really wonder why he didn't used them during the dream. I hope the author hasn't forgotten about it

Well, no surprise there. He is actually Satan

He has good in-ground intelligence but has terrible post battle and pre-battle skills. Once again he is saved by his plot armor

He should have followed Gilles' route and gone to the sewers. Sometimes his skills feel like decoration, doesn't he have clairvoyance as a class skill? How could have Emiya followed him? There is a difference between been normal and being incompetent

I understand that he is very inexperienced but at this point the only thing keeping him alive is plot armor

Well, he did plan an escape route. He is not completely useless, at least. I just hope that he is able to hides his traces

Wasn't Gilgamesh already summoned as an archer? How was Emiya summoned then? Did he come an assassin?