For Jaseb, if you are happy to pay $5900 one way, you can have the coveted window seat in JAL J Au - Japan.
Others say you could till OLCI to see if these window seats open up, but they are probably coveted, and JAL knows it.
Only way to guarantee if you want a window seat, is to stump up for the $ and buy it outright.
I see that flight leaving a bit past midnight, as good, as it gets you into Tokyo at 8am or so, early enough to spend some quality daylight time in Tokyo before hotel checkin.
Also gives a bit of time if you finish work at 5pm, and get to MEL Tulla T2 to spend some time in the Maharba, or the QF J/F lounge if you have access.
Or some time to fly from other state capital to get to meet that past midnight departure.
I do realise that yours is most likely a points redemption, but if you can afford it, and don't want to loose the window seat, maybe pay that premium price.
In the end, other than paying that much, I am not sure how to guarantee it.
I am looking into paying that premium when I do make it, ie, to fly overseas again.