Guardians of Oboro

Defender
Modified creatures you control can attack as though they didn't have defender. (Equipment, Auras you control, and counters are modifications.)

Mountain

Imperial Oath

Create three 2/2 white Samurai creature tokens with vigilance. Scry 3.

Eiganjo Exemplar

Whenever a Samurai or Warrior you control attacks alone, it gets +1/+1 until end of turn.

Plains

Tranquil Cove

This land enters tapped.
When this land enters, you gain 1 life.
{T}: Add {W} or {U}.

Island

Akki War Paint

Enchant artifact or creature
As long as enchanted permanent is a creature, it gets +2/+1.

Seven-Tail Mentor

When Seven-Tail Mentor enters or dies, put a +1/+1 counter on target creature or Vehicle you control.

Peerless Samurai

Menace (This creature can't be blocked except by two or more creatures.)
Whenever a Samurai or Warrior you control attacks alone, the next spell you cast this turn costs {1} less to cast.

Swiftwater Cliffs

This land enters tapped.
When this land enters, you gain 1 life.
{T}: Add {U} or {R}.

Imperial Subduer

Whenever a Samurai or Warrior you control attacks alone, tap target creature you don't control.

Moonsnare Specialist

Ninjutsu {2}{U} ({2}{U}, Return an unblocked attacker you control to hand: Put this card onto the battlefield from your hand tapped and attacking.)
When Moonsnare Specialist enters, return up to one target creature to its owner's hand.

Sky-Blessed Samurai

This spell costs {1} less to cast for each enchantment you control.
Flying

Norika Yamazaki, the Poet

Vigilance
Whenever a Samurai or Warrior you control attacks alone, you may cast target enchantment card from your graveyard this turn.

Heiko Yamazaki, the General

Trample
Whenever a Samurai or Warrior you control attacks alone, you may cast target artifact card from your graveyard this turn.

Blade-Blizzard Kitsune

Ninjutsu {3}{W} ({3}{W}, Return an unblocked attacker you control to hand: Put this card onto the battlefield from your hand tapped and attacking.)
Double strike

Invoke Justice

Return target permanent card from your graveyard to the battlefield, then distribute four +1/+1 counters among any number of creatures and/or Vehicles target player controls.