A US soldier/mercenary in a slightly alternate history ends up in the body of a Japanese high school boy who's sister-in-law wants to marry him one day.

Oh and he buys a Beretta off the dark web (WHICH HE BRINGS TO SCHOOL and how the hell did he hide it in a school blazer?!) and convinces his old mercenary buddy that he's reincarnated and makes a merc team that shoots bad people up and in this world organ transplants can transfer stuff from the donor and even change the recipient's skin... more>> color (what) and some hospital in Massachusetts "has produced more than 10 Nobel Prize winners" (what) and no a human cannot actually swallow a grenade and aaaaaaaaaa I can't stop my eyes from rolling! So many s*upid details everywhere.

There's also a lot of real-politics and social issues mentioned like the 2015-2016 s*xual assaults in Germany, the protag's previous life was ended by the "same" people who shot down Flight MH17, there's a few paragraphs on s*xual assault rates in the US Army and at one point the US electoral college system is discussed and what the hell even is this story.
I stress that I made not a single thing up, everything I mentioned is in fact in this story.

Real problem is, it's boring. All the characters including the MC are dull and uninteresting, the actual shooty bits are brief, poorly described and poorly written. The real life political stuff is always done via (at times rather random) infodumps even if said info has little to do with what's going on, the story's flow is an utter mess with random developments and info shoved in our faces, all of it boring.

Even if you don't mind edgy stories this isn't even good as a guilty pleasure, there's more infodumps than bullets here and as mentioned the actual action is very poorly written, it's "I shot him and he died"-tier stuff.

Edit: Don't mean to start an argument, but since the other reviewer at this time claimed I "don't like history, recent event" among things (which gave me a good laugh) including the claim that I speed read, let me say this: in one chapter a heroine is warned about s*xual assault in the US military. Immediately after this warning the author has several paragraphs on the subject including the US military's entire bullet-pointed definition of s*xual violence and a bullet-pointed list of incidents. Then we get six sentences of dialogue only for the conversation to be promptly interrupted again by five paragraphs on opportunistic homosexuality, all of which is written like a Wikipedia article or copy-pasted from some academic thing. (The author even helpfully cites sources for most of the IRL bits... one of which I noticed was a 2005 iteration of an annual/biennial report that the author for some reason picked over all the other releases since.)

So no, I didn't speed read. I will confess that my eyes glazed over slightly when the author kindly informed us readers that non-consensual sodomy is illegal in the US army. I wish I was joking. <<less

If you don't like history, recent event, just speed reading, etc like other user's comment, don't read it.

Anyway, it's a great work... I'm in the middle of it, but here are my impressions.
I found it very easy to understand because of the well thought out setting and the explanations that are provided.
The sense of realism is particularly strong, so even though the setting is creative and far from reality, there is a strong sense of immersion.