[Coldsaturn]

OS usually goes to the beta core because you can find it as main stat. On the alpha core you'd have it as substat only.
For X-02 they usually tell you to do:

Stella match: 2 Oath Strength in the 2 beta cores going to the solar cards
4 Damage to weakness to the delta cores going to the lunar cards
(when I say "2 OS and 4 DMG to weakness" I'm talking about the main stat of each core, so 2 beta cores with OS as main stat, 4 delta cores with DMGtoW as main stat)
The rest of the substats should follow based on importance: ATK bonus, flat ATK, DMG to w, OS

No stella match: 1 OS and 1 Oath Recovery; or 2 Oath Recovery for the beta cores
3 Crit Rate 1 Crit DMG for the delta cores
The rest of the stats should follow based on importance: ATK bonus, Crit Rate, Crit DMG, ATK flat, OS