As an update, great stay at the hotel. Really one of my first Hilton stays which exceeded expectations.

1. Rooms look nicer in person than website (Tripadvisor/Hilton)
2. Bathrobe in the form of night gown. Really comfy, and stops people wearing it to the pool ?
3. Toiletries, Slippers, Night gown automatically replaced daily.
4. Had to extend another night due to flight "retime" , front desk were quick to use the lowest rate (from my existing stay) instead of website rate. ~10k yen savings/room

For multi room bookings :
Diamond benefit extended to 2 rooms (4 pax total), including bfast, lounge & pool access.

All rooms were standard and received upgrade to bridge view.

I emailed the hotel beforehand, reply was that only 1 room would receive Diamond benefit. However checked in at Front Desk and automatically handled room keys with Welcome letter & Diamond benefit. Did not do OLCI as was showing standard rooms.

One thing I noticed was the different toilet layouts in the rooms. Had 4 rooms, and 3 had different toilets. 1 Twin had no rain shower + basic water controls, while another Twin had rain shower + separate temp/pressure + shutters looking into room. King had the same but a completely separate shower. Otherwise fittings were all similar and wouldn't have minded either type

All in all, a great stay with easy access (but ~30minutes) to most of Tokyo's attractions. Many things around the hotel itself, along with 24h convenience store + 24h McD or Jap fast food (beef/pork rice bowl).