I think this is the discipline you take unless you have a key and critical use for one of the other three, even if you are mainly going to focus on weapons and fighting with lily I would still advise taking this discipline first for one reason that trumps the other three.

Alignment of spirit can be flipped back incredibly reliably, being basically immune to your personal weakness is a good move to have before you get your XP. (made even more reliable with deny existence and other damage cancellation cards)

The other two side benefits are pretty plain too, healing on any turn where you take damage/horror and +1 to the most commonly tested defensive stat are both good for surviving longer on average, a fighter who survives longer and has more health can keep the rest of the team alive long and earn those juicy juicy victory points more consistently, which gets you to a more flashy discipline.