To build these relationships — called Confidants in Persona 5 — the protagonist can interact with the various characters that will provide new skills and resources throughout the game.
One such character is Tae Takemi, the doctor who runs the clinic down the street from the protagonist's home. Takemi is associated with the "Death" Confidant and improving your relationship also grants access to a larger variety of healing and support supplies. If you want to be able to take down palaces more efficiently, getting to know Takemi is important.
Persona 5 Tae Takemi Confidant Guide: Building a relationship with Tae Takemi
Since she is always at the clinic, building a relationship with Takemi is fairly simple. She'll always want the protagonist as a lab rat for her new experimental medication. The downside? You'll need to build your Guts stat in order to get further in the testing trials.
Between interactions with Takemi, you might want to go to the diner to study or read a gutsy book on the train to improve your stats in preparation for the trials.
If you're able to build that relationship — and by extension increase the rank of the Death Confidant — you'll be able to buy important items that will replenish your HP and SP, and eventually buy items that will revive fallen allies in battle.
More Persona 5 news, updates, tips and tricks
For more on the latest entry in the Persona series, check out the rest of what Mic has to offer. Here's a guide on how to capture Personas, and here's one on building relationships with the game's Confidant system.