Seriously asking if any of the western ships didn't arrive in Japan, then how did the Japan here looks so much like the Japan now.. if there's no western ships how did the Japs got guns and etc, since firearms came from outside Japan and got imported to Japan, and Oda Nobunaga would not get his gun from the dutch or portuguese and possibly lose against Takeda in Nagashino battle because of that Toyotomi Hideyoshi will not unify Japan. And since they said they became isolated because the sea changed they should have less technological advancement than the current one. The reason Japan could catch up with the rest of the world was because Perry (America) forced the Japs to open up border and import a lot of knowledge and once Japs catch up with the rest of the world they use it to wage war with the surrounding nations to acquire resources to boost the Japs growth in the late 19th and early 20th century.
The world building are good but it didn't make sense if they make the sea couldn't be crossed, they would still have medieval era technology if it did. The solution of this would be that maybe there are other people that are reincarnated here from modern Japan long before the MC born. But well it's fiction.. I will enjoy it since for now the story and the art are good and it's free too (Can't complain about it).
Anyway as always thanks for the chapter, and thank you for bringing it here.