I'm about to start Ruby Phoenix and while I want to play a Summoner I'm still undecided about what type of Eidolon. Keeping with the theme I thought having a something resembling a Kamaitachi might be cool.
For those unaware a Kamaitachi is a Yokai from Japanese mythology that looks like a weasel with sickles for feet and sometimes it has one for a tail. They are associated with wind as well with some even being able to fly.
I did see they showed up in Bestiary 6 in the previous version as a Fey but that version was more cunning and was about using it's abilities to torment characters where I see the Eidolon as more a speedy attacker.
I guess my question is would it be better to pick the Beast Eidolon if I just want to play an attacker or the Fey since it has more varied options but potentially less attack power?
What do you want it to do when the battle's tough? When facing the BBEG?
If it's melee, go Beast, the difference is large IMO (though by the higher levels of Ruby Phoenix, that gap could narrow a lot).
If it's Fey stuff like spells, Demoralize, etc. then go Fey and they can hold their own at range too.
Which is to say, Beast is what you should go for if you want a "speedy attacker". Ruby Phoenix can give some good opportunities to buff for the tournament (favoring the Fey), so there's that, but I expect most of the combat will occur outside the arena (much like in the module).