This recipe has the light taste of komatsuna greens. It keeps well because of the ume, so I recommend this for bento.
Since we're expecting a baby now, I try to eat a lot of komatsuna because it's full of nutrients. Ume helps boosts your appetite, so I added some of that, too.
The excess water is squeezed out after boiling, then again after marinating in soy sauce; do a good job to squeeze all the extra moisture out! If you squeeze it out well, it won't get watery later.
Enjoy Japanese food around the world.