This is interesting and a new application of this type of communication. The graphic really buried the lead though. I've added some notes in RED that put it into proportion:

JAXA is receiving a signal from point A on Earth in a "close satellite" that is only a few hundred kilometers above the surface of the Earth in LEO (Low Earth Orbit). The "close satellite" is then sending the data via laser away from Earth to the "far satellite" about 34,600km behind it in GEO (Geostationary Orbit). The "far satellite" is then turning around and shooting that back at a different point on Earth, point B. Pretty cool stuff!

Note, the data rate is pretty high here 1.8Gbps, but because they're shooting out to GEO and back, the latency takes a big hit. We're talking about 500ms of latency. We're facing the limitation of how slow the speed of light is here. Keep in mind, for the application here that JAXA is doing, big data dumps, latency isn't really an issue. You pay the one-time (and one-way) latency cost only once when you start the transmission of data. So if you were using this to download a large file which took 10 minutes to download at 1.8Gbps, with the latency costs its only going to take 1/4 of a second longer through this satellite link for the GEO portion of the transfer vs two systems sitting 1m away from each other on a desk on Earth somewhere.