IIRC Air Japan is changing from a sub-brand (basically a charter operation of NH) to its own separate branded entity, but I can't recall if this is really going to happen or when, but I recall reading something about it adopting a true LCC model, different from the Air Japan that most of us are familiar with which is nested inside ANA. Unless something changed, the ANA 787-8 has angled lie flat seats in business, not true lie-flat seats - I've flown in them many times, but not recently so perhaps that's changed more recently. If the OP is flying NRT-SIN, they may end up with angled lie flat instead of true lie-flat - but maybe someone who has flown them more recently can confirm if this is still the case.

Having said that, from a service and quality perspective, coming off the UA 777 and onto the NH 787 will be like stepping out of Target and into Neiman Marcus, bed seat or not.