To obtain the Overprotective Achievement in Lovers in a Dangerous Spacetime you will need to unlock the ability to place two gems in the shield station. To do that simply collect as many lost friends as you can in each level to unlock it early on. Once you've done that you'll need to place a beam gem and metal gem into the shield station. The metal beam shield will absorb shots which adds a cell to the shield and you must have 20 cells on the shield at once to unlock the achievement. The trick is finding an area where the enemies won't run into them and keep moving the shield around in order avoid damage but to also catch projectiles. Try to have enemies on all sides preferable land based ones that won't run into your shield. Also you'll need to have enough so they can shoot it quick enough to build it up before they eventually disappear. Easier said than done but hopefully the video will give you some help.