I'm looking for a manga where a character is sent back in time (or another world with less technology) and has great technological knowledge and uses it (i.e. invents primitive versions of future tools like making guns in medieval times or creating electricity and light bulbs).
I have never found a manga that has this even though it is a classic idea.

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All choices are made in fear,
What you fear more is the only difference.
Positive decisions are made in fear negative consequences,
Negitive decisions are made in fear of positive decisions not giving the outcome you want.
Embarrassment is the fear of people knowing your real thoughts.
Greed is the fear of having too little.

Demonblaze0's personal thoughts

Ryuurouden kinda fits but not exactly other than this, i don't really recall any.

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“I’m tempted to kill the general first, then his staff officers. Sometimes you just want to eat pudding early. All the same, I make myself wait.”

“The good guys fight for freedom, justice and most words that don’t put food on the table. The bad fight to scrub those words from our speech. Only problem is, both sides claim to be good.”

Jin focuses on a modern surgeon who went back to time and used his medical knowledge (e.g., penicillin, brain surgery, surgical tools and procedure) in dealing with the pandemic that happened in Japan. At the same time, he changed the medical history as the first person who 'invented' the penicillin. I havent read the manga though, but I know this from its live-action adaptation.

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Rape is imminent.

jin looks interesting, to bad no one has translated it

Japan was slow to give up the 'way of the samurai' after newer technology existed. using a gun was deemed dishonorable, death was officially preferable to dishonor, so there is little regret in not having a newer gun, or modern technology when looking at the past.

Japan likes giant robots because they are a form of technology that can use a sword. There are numerous series with robots from a more advanced time come to a place without them and change the landscape.

but never guns, because in anime Swords > guns.

There might be something like this in Amagoi later (it seems to lead that way), but not much so far.

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"Thus is our treaty written, thus is agreement made
Thought is the arrow of time, memory never fades
What was asked is given, the price is paid"