From Mangadex:
Spin-off from History's Strongest Disciple Kenichi. Note: Only read this manga once you're up to at least chapter 313 of Kenichi main series. Released at the same time as Kenichi volume 48 (containing chapters 448-457), Kenichi Plus is a collection of three short stories that will take us back in time… The first story features Tanimoto, as he kindly reminisces his memories of Kano Shou, from the first time he met him, up until Kano Shou last fight… In the second story, we follow Loki and No.20 adventures, as they start and struggle to run their detective agency. But that's when Niijima shows up with a request that fit them perfectly. For the final story, which features Renka, we will follow Pisuke's story, a bird who lived many adventures before ending up as Renka's pet