Myrrh, Frankincense, and Steel: Kurald Galain's Guide to the Magus

[Yanisa]

FYI half-elf trade skilled for ancestral arms, not elven immunities, so you can get both EWP and +2 to will.

Both race traits swap out Adaptability, sadly.

Ancestral Arms Some half-elves receive training in an unusual weapon. Half-elves with this racial trait receive Exotic Weapon Proficiency or Martial Weapon Proficiency with one weapon as a bonus feat at 1st level. This racial trait replaces the adaptability racial trait.

Dual Minded The mixed ancestry of some half-elves makes them resistant to mental attacks. Half-elves with this racial trait gain a +2 bonus on all Will saving throws. This racial trait replaces the adaptability racial trait.

Kensai get Exotic Weapons from class, so they can do both, in a sense.