I can already see whats going to happen, he's going to find a way to restore her sacrificed lifespan and also prevent her powers from taking any more, and thus she will be so thankful she'll become his waifu.
There are different levels to it, translating a copyrighted work and distributing it for free is indeed copyright infringement since the copyright holder is "losing" sales, usually distributors look the other way since fan-translations bring their work into markets it otherwise wouldn't reach.
Selling another persons work when you don't have the right to however is a nice way to get arrested.