I'm going insane trying to remember what the title is:
In the first chapter it was a guy who was originally from a Hi-Tech future fighting aliens? He then blows up everything with himself since all his comrades died and then found himself reincarnated into a fantasy world as like a 15/16 yo lord (blond haired). Then typical fantasy male lead stuff happens.
What I liked was that it was not setup for him to take over the country or something like that - it was getting sort of interesting where he meets like a Prince / heir to throne on the way while negotiating to get water from a lake from where I left off.
Using today to catch up on the progress of this at least...