The policy for mixed class redemption is that miles is charged at the rate of the highest cabin class in the redemption.

I think OP is looking for OW (since OP quoted 105k for HND-HKG-SFO in F)

However, HND-HKG-SFO all in first is 130k (not 105k) for one-way

For HND-HKG-DEL, assuming oneway, spliting or booking together costs the same miles (30k +40k vs 70k).
Benefit for spliting is 1) you can tag something after HND-HKG, e.g. TPE, if it is potentially useful; 2) you can cancel your HKG-DEL even if you have flew HND-HKG.
Benefit for booking together is 1) in case you need to cancel or reroute the entire trip, you pay the relevant fees once only.