Sanosuke is sent to the manga/anime universe of Berserk, the scenarios are as follows.

Scenario 1: Sanosuke takes Guts' place as the main character of Berserk, he is found at the three with hanged corpses like Guts was, and things go from there, joining the band of Hawk and so on up until the current volumes of the manga.

Scenario 2: The plot gods place Sanosuke at the point of Berserk where Guts got the Dragon Slayers sword, he's in his place as the main character, he is given the same things Guts had when he first went, including the Dragon Slayer.

Scenario 3: Sanosuke is Raised with Guts as his brother when they are found at the three with hanged corpses.

Scenario 4: Sanosuke is placed at the point where Guts' gets the Dragon Slayer, there he sets out with him.