I think I’ve found a workaround for obtaining trophy. Yesterday I was able to claim it.
If you have the Dragon Pack from the Digital Deluxe pack it gives both Naoe and Yasuke a legendary headpiece and body, as well as a trinket and one weapon (katana & long katana)
Based on that you only have to obtain a few items. Tanto. Kusurigama. Naginata. Kanabo. Teppo. and Bow. All these can be found in the open world once you get into the open world with Naoe. You don’t even have to obtain Yasuke.
Turn on guaranteed assassinations. You can kill all Daimyo with the hidden blade or Kunai
Tanto—Masamune’s Thorn—Location: Nochiseyama Castle (Wakasa)
Kusurigama—Bloodletter—Location: Kashiwara Fort (Iga)
Naginata—Time Honored Crescent—Location: Kashiwabara Fortress (Omi)
Kanabo—Tremor Strike—Location: Yakami Fort (Tamba)
Teppo—Dynasty Ender—Location: Genbao Fort (Wakasa)
Bow—Funeral Pyre—Location: Inariyama Garrison (Harima)
Alternatively—you can use the in game keys and obtain items from the Animus Exchange and whatever you don’t purchase (due to item rotation) find in the open world.