Broccoli is new to me (as is most gardening, to be honest), so I went back and did some reading about the plant species and this particular cultivar. I made a mistake in originally calling this particular variety "gai lan". Gai Lan is similar to kale with smaller, edible leaves. The particular cultivar I am growing is probably (though I'm still not 100% confident) called "sprouting broccoli".
Interestingly, most of the sources I've read point to broccoli being a cool weather plant. Cool autumn and spring weather in the low teens (°C) are perfect for it. The informational label says the plants will be edible within 3 months, so hopefully spring sticks around for a while. The weather has been relatively cool lately with lots of rain. There have been a couple days of sun, but the temperatures haven't gone above 20°C in Tokyo yet. I had always assumed it was a summer plant.
I moved the pot off the veranda floor onto the A/C unit outside. We don't use the A/C, so it's more of a shelf than anything else at the moment. Raising it up higher also exposes the broccoli to more sunlight which I hope helps it grow.
The stem is still very thin. In the past two weeks we've had some very strong winds which have resulted in the broccoli stem bending at the base. Most broccoli that I've seen have at least an inch thick stem, I'm left wondering if the stem will increase significantly in girth in the next month.
In this picture, you can see the floret hiding in the middle of the stalk.
You can also make out some green strawberries in the planter behind the broccoli. The one in particular I took a picture of last week is now twice the size!