This only appears after you fight Eir in Stranga but it's a lot of fun to do in casual play too! There are two techniques I'll discuss here, Seed Carry and Seed Juggle.

Seed Carrying is a quick way to use your blaster to move the seed diagonally upwards, as demonstrated in davidki's Any % run. It's a bit tricky to pull off, especially if you're not the fastest shooter, but you essentially fire at the seed point-blank and hover upwards at the same speed. Because you're shooting it forward, you must also hover forward to keep up. This saves time in reducing sub-weapon switching and positioning.

Seed Juggling is more of a novelty. To juggle, you approach the seed and fire twice--again, point-blank--to get it in the air. Immediately, you lock diagonally up and fire to keep it there. You will need to keep forward to start it but once you have it going you don't necessarily need to maintain speed to keep it up (although you will still need to inch forward regularly). Some may find this easier to pull off than Carrying. Though it isn't the most optimal technique, it's still faster than the intended way of moving the seed. It requires a lot of horizontal room to do well, so the first seed room is the only practical place for it in a run (unless someone manages to pull it off in the future). The real value of the move is in how fun it is to do! Try for a long combo or try to see how high you can get it!

The first seed room in Stranga (the one where the flower takes G-Sophia) is a good place to practice both of these.