SCARLET NEXUS

The first person you can get a Level 6 Bond with during Yuito’s play through is Hanabi and that will be possible on Standby Phase 8 (credit to ImaginaryRuins)

I personally had Tsugumi as my first during Standby Phase 9, it’s more likely because I used her and Gemma in almost all my missions and side quests when I was playing as Yuito. Hanabi is available earlier than both of these characters so that’s why the method above is faster.

(Check bottom of text to see Kasane’s)

You must complete all the 5 Bond Episodes for the first 5 levels and then give all the gifts to Tsugumi to get the 6th level. These gifts will periodically become available as the game progresses, use the supplies to exchange for the gift at the shop. Always farm some enemies by doing the side quests also and you shouldn’t have an issue getting the supplies. Also, the more missions/quests/free roam farming you use them in, the faster it’ll progress. This mostly benefits the first 4 levels where the margin for each level is still small.

I don’t know who the first person is for Kasane’s run just yet, but the concept is the exact same: do all 5 bond episodes, and make sure to give all gifts. The timing in the story is most definitely the same, during standby phase 8 (Will update on the person once I get there).

Not sure how difficult this will be in the long run - but keeping people in party and using their abilities will increase bond level. That, and giving gifts. Some people are story gated so this may/may not be missable.

In terms of gifts, these are the optimal items:

Hanabi Ichijo – Rare Antique Lamp
Gemma Garrison – Famous Select Alcohol Set, Sandbag
Luka Travers – Toys, Exercise Equipment
Tsugumi Nazar – Plants
Kagero Donne – Guitar
Shiden Ritter – Cleaning Items