The achievement is unlocked for recovering 100 bodies. Occasionally, you will come across android remains. If you interact with the remains, you 'pray' for them giving you the opportunity to recover them. If you choose to recover them, you will get some gold and some temporary stat boosts. These remains are available online and offline. If playing online some, but not all, of the remains will represent other online players. If you die and recover your previous body, this will count towards the achievement.
The remains become available in chapter 2. It is possible to grind for them but this is a long and tedious process. It is not necessary to grind but the first fairly good location is in the Desert Residential Area midway through Chapter 3. There are always two bodies provided by the game on the way to the pit where you encounter the chapter 3 boss. You do not have to pray over the bodies. Just interact with them to collect them. If you want to grind for the achievement, go back a short ways until you can save. Make sure you activate the desert residential save station. Then, you can save and reload the save file. The two bodies will respawn and can be collected again. Although this is a reliable method, it is still quite painstaking. Eventually, in the normal course of play you will get up to 100 bodies recovered.
You can see your approximate progress by checking the 'Bodies Collected' count in Play Records under System. This stat will not include the number of times you have collected your own body. It will also not include bodies that are collected without the opportunity to pray over them. There are always two such bodies in the Desert Housing Area. It will accurately reflect the number of other remains you have collected after praying over them.
Note: It is of value to recover these remains and, by the time you have done 3 playthroughs, you will almost certainly have recovered 100 bodies and unlocked the achievement. This is particularly the case because there are over 100 bodies to be recovered in the Copied City alone during your first playthrough. You will have to do some evasion because you will be recovering most when fighting. However, since the action stops during recovery, this is not difficult. Nevetheless, the achievement is available for sale for 100,000 gold at the secret achievement shop. This special shop becomes available after three playthroughs.