Demon Slayer: I Became Shinobu Kocho's Older Brother

The protagonist's abilities: travel through time and space + knowledge of some of the plot + sympathetic comments from viewers in a parallel world. No breaking up canon couples, one female lead, Shinobu.

This story focuses on redemption: redeeming people (Kanae) and demons (Akaza, Koyuki, and the siblings Daki and Gyutaro).

His soul transmigrates into the Demon Slayer world, and just as he's about to starve to death, he's successfully adopted by the Kocho family and given the name Kocho Toru. But Toru is panicking. He knows some of the plot, and knows his adoptive parents will be killed by demons. Guys, what do I do? I don't want them to die. Luckily, his golden finger activates, sending him to the Sengoku era, where he meets someone at the very peak of Demon Slayer's power rankings.

The story roughly follows this order: the Yoriichi arc and the first Demon Slayer Corps members; the pre-Hashira arc with Kanae and the Wind Hashira; the Taisho era; the Entertainment District arc with Daki and Gyutaro; the Infinity Castle arc and the rescue of Soryu; life after the demons are gone; and possibly the return of demons in the modern era and how the descendants of the Demon Slayer Corps will fight them.

The story is now in its final volume, focused on rescuing Soryu.