Nihei's Venusaur is Nihei's main Pokémon that lives in the ninja village. When Sanpei returned to visit the ninja village, Nihei's Venusaur had a battle against Sanpei's Greninja to show his brothers the results of his studies right away. Nihei also said he wouldn't go easy on him.
Hanzo noted that Sanpei's Greninja fighting against Nihei's Venusaur meant that Sanpei had a disadvantage but nonetheless fought on an even level. Although, it wasn't enough to win the battle as Nihei's Venusaur was able to contain the damage to a minimum and waited for a chance to turn the tables.