from what I know they work similar to weekly events in that they show up for a bit then there gone for awhile then they come back though I dont think seal and free pull carry over. as for what to pull we dont have Han or Utakate translated so I don't know bout them but the most useful in my opinion would probably be Yagura since he hits through super armor but that just me.

We do have Utakata and Han translated. Even Edo Fu is translated

Han [Edo]

Mystery: Becomes Immune to debuffs. Increases Crit Chance by 15%. Gains 3 Additional Standard Attacks

Standard Attack: Attacks a random line of opponents. Has a high chance of causing Repulse and Ignition.

Chase: Chases Low Float causing Knockdown. Reduces CD of mystery by 1 round.

Passive 1: Whenever this unit takes taijutsu attacks, The attacking unit will suffer from ignition, while this unit's attack and defense is increased.

Passive 2: Before an action, gain life based off its ninjutsu. Also has Super Armor.

Utakata

Mystery: Causes Water Attribute Damage and slow to up to 3 units. The Selected unit will suffer from knockdown. While the selected unit is suffering from slow, deals water attribute damage to up to 3 units.

Standard: Attacks and damages a random unit. has a chance to remove all shields and buffs also causing slow.

Chase 1: Chases and attacks knockdown causing repulse. Gains a shield based on 20% of this unit's resistance.

Chase 2: Chases 20 combo causes 4 units to be ignited.

Passive: Before first action gain life based off the ninjutsu also becomes immune to debuffs.