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Well that was a battle but Wales showed real grit to come through in tough conditions against a team higher in the world rankings.
Seren Lockwood scored twice, either side of a try by hooker Kelsey Jones, but it was the defence that impressed most with a first clean sheet for almost eight years.
Alex Callender celebrated her 50th cap in a huge display by the Welsh pack in the second half.
But the result was tainted by what looks to be a serious leg injury to centre Freya Bell who will almost certainly miss next week's follow-up match in Kumagaya.
So join us again next Saturday for live coverage of the WXV.
Elinor Snowsill
Former Wales fly-half on BBC Radio Wales
Wales really needed that try before half time, there are still some concerns but at least they've given themselves a seven point buffer.
The coaches will be speaking about their discipline, they've got to get back on the right side for the ref, Kate Williams and Alex Callender have to try and talk to her.
Philippa Tuttiett
Former Wales international on BBC One Wales
From a Welsh perspective, they've got to be quicker at the breakdown, the Japanese team are straight in over the ball.
From Japan's perspective, they need to look to utilize their kicking game, they've got some fast players on the outside edge.
PREVIOUS MEETINGS
2021 Wales 23-5 Cardiff Arms Park, Cardiff
2024 Wales 19-10 Athlone Sports Stadium, Cape Town, South Africa
This will be their first meeting on Japanese soil.
Wales have won both previous tests between the two teams, the most recent coming on neutral soil in South Africa during WXV 2 2024.
Tries from Nel Metcalfe and Keira Bevan gave Wales a 12-0 lead after 15 minutes and it would remain that way until half-time.
Jasmine Joyce grabbed Wales’ third try shortly after the break with Bevan’s conversions taking it to 19-0.
Japan had to wait until the final quarter to open their account with tries from Misaki Matsumura and Ayasa Otsuka.
Joyce had also scored twice in the first test between the sides in Cardiff in 2021.
Japan ran out 52-10 winners when the sides met in a non-cap match in June 2017 in Ystrad Mynach when Iroha Nagata and Keiko Kato each scored a brace of tries.
The sides will meet again at Kumagaya Rugby Stadium on 31 October.
The half-back partnership of Seren Lockwood and Keira Bevan that stretched the South Africans has been restored and Nel Metcalfe, a livewire highlight at full-back in the 2025 World Cup, returns from injury on the wing.
Her sister Branwen packs down next to fellow bright prospect Jorja Aiono in a mobile second row, with the well-balanced trio of Alex Callender, Kate Williams and Georgia King in the back row.
Wales: Neumann; N Metcalfe, Cox, Bell, A Williams; Bevan, Lockwood; M Davies, K Jones, Tuipulotu, B Metcalfe, Aiono, K Williams (co-capt), Callender (co-capt), King.
Replacements: Reardon, Pyrs, E Jones, Crabb, G Evans, B Lewis, George, Keight.