So far, we've only seen 3 Feat of Arms (Noble Phantasms
):
Akigase Rikka's Onikiri Yasutsuna: Onigiri no Tachi
- user can cut down Legions by themselves
Tachibana Masatsugu's Izumi-no-Kami Kanesada: Gankouken
- grants any Legions under control with katanas (probably made of spiritual steel, folded 10000x) and Tennen Rishu sword style
Sir Black Knight's Archers of Crécy
- grants any Legions under control with big black longbows
I look forward to what the other Returnees can use as their Feat of Arms, especially Julius Caesar and Richard the Lionheart.
The former, probably related to Crocea Mors and "veni, vedi, vici".
The latter, well... related to lions probably.