Maybe not completely a prequel because I do think this is after the other story (Reika's older) but I think it partly is considering that it tackles Rogi's past with the third head.
I think the flashbacks are kind of prequillish, whereas the rest picks up three years later--probably after the time Reika ran away in the other story. http://www.mangago.zone/read-manga/yondaime_ooyamato_tatsuyuki/mi/c008.9/pg-1/
This is three years later than the beggining of Yondaime Ooyan and if I am not wrong, currently where chapter 13 ended. The past is about Rogi-san and Tatsuyuki's dad. So this is the first time we've seen Hachi.
That would make sense..especially since he is older when Hachi is around..I just was wondering where in the timeline the rest of the story fell..thank you much everyone for your knowledge(๑•ㅂ•)و✧
i really think i like this though..i like them together...this is supposed to be a prequel right? It didn't seem like the "dog" was still around in the other story..that would suck if something happened to him =/