Kamen Rider Companion Builds

Jormangandr/Kamen Rider Arsenal Left Gauntlet
Good Samaritan (free) Kinda, he's not very good at it
Reach My Hand Out (free) Apparently painting vivid images of how much worse things could be helps
Nothing in This World is Useless (free)
Two In One Jumper (400)
Windscale Hat Collection (free)
Prism Driver (100)
Known Wanderer (0)
Honestly went Samaritan because I found it funny. Ended up with a quite nice set of improvements for him though. The Prism driver especially is great when you've got two people actually used to being weapons. Jormangandr will be a bit odd in how he expresses some of his perks here, but the end results are the same.

Anubis/Kamen Rider Arsenal Right Gauntlet
Good Samaritan (free) Even worse at it than Jormangandr
Nothing in This World is Useless (free)
Reach My Hand Out (free)
Two In One Jumper (400)
Medagabyru (200)
Superior Combination (0)
Anubis is probably the best suited to Arsenal, both due to perks and past experience. He's a bit of an odd fit for Good Samaritan, but some of his misadventures in the Land of Frogs and  Wind have helped to mellow him out. He's got a decent feeling for which memories would work well, which is important when there's loads of them to choose from.

Hyuga/Kamen Rider Arsenal Left Half
Creative Mind (free)
In the Right Hands (free)
Professional Quirks (free)
Clear Memory (400)
T2 Gaia Memory Set (200)
Identity Hiding Disguise (free)
Briefcase of Gaia Memories (0)
The Hyuga provides the actual Memories needed for Arsenal, while also serving as a part of it herself. The disguise will also be useful for her more covert activities.

Sechs/Kamen Rider Arsenal Right Half
Drop In (free)
I've Covered Wars You Know (free)
Working in the Shadows (free)
How Prototypical (400)
Cool Jacket and Shades (free)
Bowl of Never Ending Undon (free)
Memory Gadgets (200)
Claws Personal Type (0) Cutter Wings
Sechs provides combat ability and flight to Arsenal, while also supplying some useful gadgets he picked up somewhere. There will probably be some dissonance between his and the Hyuga's fighting styles early on, but that's what practice is for. I shudder to think what Arsenal will be able to bring to bear after I deal with Unlimited Colors.

Bigby
Made Man (free)
Ride Out! (Free)
Sealing the Deal (free)
Right Hand Jumper (300)
Read the Manual (200)
Birth Buster (0)
Bigby is sadly on the sidelines for this one. He gets some useful items out of it though, and the Birth Buster is some decent firepower for if it becomes necessary. Mostly he'll be serving as an aide to ensure everything on the mundane front stays functional. Going to be needing some interesting infrastructure to start producing Cores.

Desty Nova/Kamen Rider Nova (Bit lazy, but it fits)
Inquisitive (free)
Making an Impression (free)
Terra-Fying (free)
Knowledge is Power (300) One Karma Memory, coming right up
Digging Tools (free)
Infinite Cake Ingredients (free) I hear rumors he's planning on creating a flan cake
Lux Driver (100)
Let's Start the Lookup (0)
Desty continues to be the mad genius we know. Was conflicted on which Inquisitive capstone to give him, but it worked out decently. Lux Driver was mostly because there wasn't anything else I felt like spending the 200 on.