Quick one for you guys.

1. Character is participating alone
2. A Legion of One is played and targets this character
3. +3 bonus is gained. Yay!
4. New characters are moved into this conflict
5. ... ?

My understanding of the wording of the Legion of One card, and the fact that the single character participation limit is part of its cost (i.e. before the dash) makes me believe that the character will not lose its bonus once new characters move in.

Is this correct?

Yes, it’s correct. The “choose a character that is participating alone” is a target restriction, checked just the first time the ability is played. Then it comes the part after the dash, the effect, that states that the +3 bonus duration is “until the end of the conflict”. Even if that character is moved home, even if other characters enter the conflict, i will still have that bonus.

Excellent, I got it right. Thank you!