Lazy Galaxy: Rebel Story

After reading and watching other guides and comments, I have decided to compile a full walkthrough with steps and some additional notes that may be helpful
You have 6 allies:
1) H-34-RT (robot, this ally is automatic)
2) Jack (old man)
3) Simon (green gator)
4) Unkillable girl
5) Gustar Von Knittenberg (Lizard)
6) Brute (Brown owl pirate)
7) Zarg O’ Moto

Steps:
1) Complete the game to recruit allies 2-7. You automatically have Ally #1 (this robot will count as progress towards the achievement).
2) After completing the game, select story or normal mode. I chose normal mode.
3) Select ship
4) Select 1st Ally
*This is the ally that you are going to try and max-out
*In bottom right corner, you will see “dialogue history” as a cassette icon. Select this to see each allies progress indicated by a red progress bar
*Each ally develops a relationship with the other 6 allies. To see each of these relationships, select that character and then move your cursor over the other characters. Progress for each of these is indicated by hearts. You will want 4 hearts for a maxed-out relationship.
*Once a character has a maxed-out relationship with every ally, that character will have a fully red progress bar under their portrait screen.
*If you back out from the dialogue history to the select ally menu, a character with maxed-out relationships with every ally will also be indicated with a yellow star in the top left corner of the character portrait.
*Note that the 1st ally that you are trying to max out will take the longest because all dialogue options for both H-34-RT (your automatic ally) and the ally you are selecting will appear. For instance, if you choose Jack (ally you are trying to max out 1st) and Simon, you will see dialogue for H-34-RT, Jack and Simon. Once you max out H-34-RT and the ally your 1st ally, progress will
5) Select 2nd Ally
*These choices will rotate the other 5 allies that you are trying to max out with the 1st ally.
6) Play to the cutscene (you will also see a power-up floating in space there)
*If no cutscene occurs when you see that power-up, your allies have exhausted all dialogue options with each other
*Dialogue will now ~10-20 seconds. Most of it was about their history like I caught some weird dialogue between Unkillable girl and Zarg O’Moto with Zarg wanting to be a video game designer but his parents not approving….you can really tell that the game designers were padding this game with extra content to make up for its short story mode.
7) Let cutscene/dialogue play out
8) Hit “start” on your controller, then select “menu”, then select “yes”
9) If you select “continue last”, you will resume with the characters you chose so you do not need to go through steps 2-5 above.
10) Once you have maxed out 4 allies (H-34-RT is mandatory; the other 3 allies are up to you), you will need to play through the entire story mode.
11) Once you defeat the final boss, you will need to move your ship over to one of the 2 icons now present on the screen and press “Y” (like you do to pick-up power-ups and upgrades) to choose an ending:
a) Charge the enemy ship (self-destruct) – you received this ending automatically when playing through the game the first time earning:
b) Turn back and join the Intergalactic Resistance Union – THIS IS THE ENDING YOU NEED TO CHOOSE FOR THIS ACHIEVEMENT.

*I understand that there is a lot of writing here (probably too much) but I was still a little unclear on how to proceed with this achievement. Other guides were helpful with getting me on the right foot and no disrespect for them, I just wanted to write down the steps as detailed as possible. This achievement will take 2-3 hours based on my experience (special note, I maxed out all 7 allies because there were only a few remaining relationships left to max out at that point and only too me an additional hour). Hopefully this guide will fully clarify everything and save you some time.
*Please comment if you have additional notes or need help with anything.

Edit (3/9/2019): Added referenced achievement link/pictures

For this achievement you need to max out 4 characters with their friendships with each character. You can keep doing the first level until they talk then quit out and do it again. Once you’ve upgraded 4 characters you need to finish the game and pick the new option

Video guide for those who prefer visual aids: