Xiaomu (Project X Zone/Namco X Capcom) - CV: Omi Minami
Bumblebee (Transformers) - CV: Daisuke Namikawa
Luluco Godspeed (Space Patrol Luluco) - CV: Mao Ichimichi
Neptune (Neptunia) - CV: Rie Tanaka
Additional Notes
About half of these are vibe-based.
I don't really keep up with the Japanese voice acting scene so I don't know which VAs to pick for the Transformers characters, since they've had multiple as opposed to most of the other characters featured here having consistent seiyuus.
Similarly to the above, Inferno Cop's seiyuu was Junichi Goto, who died in a motorcycle accident in 2020. This is why he doesn't have a voice actor listed.
Yes Usagi being a tank is a reference to the "Usagi is fat" meme
I had a LOT of Kamen Rider ideas (most notably Gunner Geats, Sprinter Double, Sprinter Ex-Aid, and a Den-O form for each class - Attacker Momotaros/Sword Form, Sprinter Urataros/Rod Form, Tank Kintaros/Axe Form, and Gunner Ryutaros/Gun Form), but ultimately decided to slim it down to one Showa character, one Heisei character, and one Reiwa character that represents the most recent series since that's the most likely route a Kamen Rider collab will go.
Luluco/Trigger-chan and Inferno Cop would be part of the same banner since Inferno Cop and Space Patrol Luluco take place in the same universe. (And so is every other Trigger work.) I don't know if Luluco and Trigger-chan would have a character change gimmick the same way Thirteen has a class change gimmick or if they'd be separate characters.
Speaking of class-changing gimmicks, maybe Decade can change his class for every Kamen Rider he turns into/Attack Ride he uses?
Radec is probably the most specific pick of this entire batch. He's a western character while the collab characters are exclusively from Japanese media, and I don't know how well Killzone 2 did in Japan, though it seems to be at least modestly popular. This is the token "I like this character and I like the game I want them to show up in" crossover pick. He would be a good character to add if Compass ever came out internationally, I think. (Also I want to see him dressed like Gustav.)
