Splashing Whale Raider

"Raidrise! Splashing Whale! An aqua current that encompasses everything around it."

- Transformation announcement via RaidRiser

The Splashing Whale Raider is a realtor who is hired by Zaia Enterprise to compete against Smile Sumida but is given a RaidRiser and Progrise Key by an unknown individual to transform into a whale-themed Raider and is the main antagonist for episode 19 and 20 of the 2019 TV series Kamen Rider Zero-One.

He was originally a human user named Tatsumi Arayashiki however due to a bit of thinking on how to beat a Realtor HumaGear his feelings were manipulated by an unknown individual which it was then given a Raidriser and a Splashing Whale Progrise Key transforming him into a whale-themed monster.

History
In episode 19 he was hired by Zaia to compete against Smile Sumida and when he's about to go to his next destination he was ambushed by an unknown individual when she placed a Raidriser on him. A while later he used the Splashing Whale Progrise Key on the Raidriser transforming him into a whale-themed Raider as he used its ability to destroy a building that Smile is about to sell to kids parents. However he was then attack by Kamen Rider Vulcan and during the skirmish he left the area with dazed Fuwa.

In episode 20 he appeared in a building with Smile ready to sale house for a lonely rich person, but he told the two that the house needs to be ready for him.

A while later Tatsumi was at a construction site as he taunts a carpenter HumaGear named Greatest Carpenter Oyakata he'd accidentally caused the bot to transform into a Magia, so he used the Splashing Whale Progrise key to transform into a Raider once again, but this time to battle the Magia and then Kamen Rider Vulcan as Punching Kong. During the fight he used the finisher called Splashing Collide to flatten Vulcan. However when Kamen Rider Thouser showed up he borrows the gorilla's ability from Vulcan to stop the fight between a Raider and a Magia.

A while later Tatsumi was at the building feeling pretty confident that he won this round, but it turns out it was Smile that won it for Hiden, so back outside he transformed into Raider one last time to destroy Aruto. However Aruto dodge his attack and transformed into Kamen Rider Zero-One as Shining Assault Hopper to battle him. After that he used its finisher to flatten Zero-One, but he dodge it and he was then freed from this state when Zero-One used his finisher called Shining Storm Impact.

Trivia

 * The Splashing Whale Raider is the first Whale Monster since the Whale Imagin from 2007 TV series called Kamen Rider Den-O.