Who do you pick & why?
To clarify, anyone with an offensive NP is a no-go so supports who also DPS (e.g. Koyanskaya, Oberon, Bride) are out.
If lucksack were guaranteed, I think I’d take someone like Van Gogh. Her NP level scaling is ridiculous, going from 50% crit to 100%. I imagine the reasoning could be her crit total is ‘secretly’ 150 at base so 150->200 is ‘fair and balanced.’ 100 base makes her good even for non-foreigners and makes her own team just choochoo even more stupidly with 460 crit (using bond CE) out the gate if both are NP5.
Otherwise it’d be Castoria as her atk buff is very easy to pop even if the scaling is normal (30->50).
As an aside whenever I search tags for fgo, jp or fluff the results are niche tags that are never used.