The theme of Death Stranding is connection, but perhaps no relationship in the game is more important than that between Sam and his BB. The BB is a "Bridge Baby," a special kind of fetus held in a suspended state where it does not age within a pod. In the game, the BB is initially described as a tool, but it's more than that, particularly after Sam realizes that he has a special bond with the BB that allows it to share memories with him. Sure, Sam is told not to get attached, but the player is going to ignore that once the BB giggles at Sam for the first time.
Maintaining a good connection with the BB is vital for Sam to continue to navigate through the BT-infested areas of his world. When Sam carries the BB, he connects it to his Odradek Scanner, which allows the BB to alert Sam to the nearest BT, and also allows him to see the BTs as ghostly shadows, which he can either avoid or launch a grenade at. However, BBs get stressed out quickly, and if they stay stressed out, they go into autotoxemia, which renders them useless in a BT situation.
This is why Sam needs to soothe the BB regularly, but Sam also needs to rest periodically in a Private Room where the BB can be recharged and updated via the Chiral Network. Here is what Sam must do to keep the BB calm and bonded to him.
Soothing BB in Death Stranding
Death Stranding will alert the player when the BB becomes stressed out. Stress happens when Sam falls from heights or gets swept away by a river current. It also occurs if Sam spends too much time in deep water or gets spotted by BTs. Finally, if MULEs or Terrorists attack Sam, it will stress out the BB. The BB will automatically begin to cry in these situations, and its stress will escalate until Sam soothes it. If it stays stressed out, it becomes autotoxemic.
It's essential to keep the BB soothed, so Sam needs to get to a safe location asap when BB starts to cry. To soothe a BB, hold down on L1 then press the down button on the D-pad. This will prompt Sam to detach the BB from his chest and look down at it. Press and hold the square button to soothe the BB and rock the controller gently to comfort it. Do this until the BB's color changes from red to light orange.
Other Ways to Soothe BB
One thing that BB loves is taking a dip with Sam in Hot Springs, which are found around the Central Region. Jumping into a hot spring will quickly improve the BB's state of mind.
If hot springs are not available, players can visit Private Rooms in Knot Cities, Distribution Centers and player-created Safe Houses. Just enter the Private Room, and BB will automatically get connected to the Chiral Network, which will restore it. If BB does develop autotoxemia, a Private Room is the only way to bring it back to a calm and useful state.
How to Bond with BB in Death Stranding
As a BB becomes more bonded with Sam, it will reduce the amount of stress that it suffers when Sam is in dangerous situations. The best way to do this is to get "Likes" from the BB, which will increase its connection to Sam. One way to do this is to interact with BB in Private Rooms. BB really likes Sam's face, so if Sam interacts with the sink in a Private Room and then moves the "L" stick, the player gets a prompt to take a snapshot. BB will give at least one like for each picture, although certain facial expressions from Sam will get even more likes.
BB will also offer Sam likes when resting in Hot Springs or passing through areas with BTs undetected. In addition, BB will give Sam likes when passing through a player-created BB sign and when Sam is driving on paved roads at high speeds.
The Otter Hood
Although BB hates it when Sam goes into deep water, there is one exception to the rule. In Episode 3, Sam will get an order to meet the Cosplay Prepper (as portrayed by Late Night's Conan O'Brien). Sam will find him next to a waterfall west of South Knot City. Take on his Orders for deliveries, and once those missions are complete, Sam gets the Otter Hood that allows him to better swim in deeper waters. It also makes Sam mimic an otter in deep water, which makes the BB happy. So when wearing the Otter Hood and swimming, the BB becomes less stressed and happier.
Death Stranding is available on PlayStation 4 and releases for PC in summer 2020.