Just found two songs that really make me think of this game. 
Connor Kauffman - Skin Of A Saint (This is what I imagine the MC is feeling/thinking when trying to work out how to deal with the whole Ace problem plus a bit of Aceās thoughts too.)
David Kushner - Hero (If the MC and their RO were in a musical you know what I mean where the pair are singing about how they really feel and the camera shows them being in different places)
For me itās this one.
Tamer - Beautiful Crime
To me itās how the MC feels about Ortega constantly āpesteringā them over trying to get back to the old days. They may want those days too, but they are in a situation where the only light at the end of the tunnel is on the path they are on. So they carry on with a grim determination despite their own doubts. Besides, no one left Heartbrake unscathed.
For me itās Hozier - āWhy would you be lovedā.
Itās literally story of my MC, his emotions, everything heās been bearing during all of his life. Guilt, pain, fear, and after HB; sense of betrayal. Itās just perfect song for him.
An anarchist mc could go great with Hells Cominā With Me by Poor Mans Poison
For me Daft Punk - Touch is a perfect fit for Sidestep, ever since the first book. The song is in no certain terms about a robot, or something alike, waking up to life. The lyrics hit hard.
Theyāre more a niche artist but 'I Donāt Know How But They Found Meās (IDKhow for short) entire thing could be described as a sort of supervillain-synth-rock-alt style, with a few songs jumping out as being very Sidestep-coded:
-SIXFT
-New Invention
-Choke
-Leave Me Alone
-Kiss & Tell
Bringing some weaboo energy into these song recs:
For a hungry scar and/or better life motivation, ''KICK BACK" by Kenshi Yonezu, aka the chainsaw man OP (I want to be happy/I want a life without struggle/I just want to mess up everything/I just want to erase everything in of your chest)
A bit more universal one, blumenkranz from Kill la Kill (Yes, I am much stronger than I ever thought/I remove withered flowers/Why do you look so sad?), though itās especially fitting if your Sidestep is not that great at being a pure villain (What do you want from me/Whether I want to or not/I must pursue the enemy/I am not yet free from this world)
Iām also hedging my bets that no matter which route I take, In The Back Room by syudou will be fitting for Revelations. Iāve already drafted the music video on my head and Iād hate to have to redo something no one else will ever see |D
Since no one else posted one yet here is a song that I think fits an Step who wants to be in the puppet
and the high and lows of it
And one for puppet/Mortum after the reveal
my Sidestep has a playlist because i kept finding songs that were perfect either for him or for the gameās vibes!
Mitski has a lot of songs that fit the bill but āCop Carā, āFirst Love/Late Springā and āA Pearlā in particular really encapsulate my Sidestepās self view and how he views his relationships with the people he loves 
The main thing Iām glad about is finally get a breather from Ortega after two books. I can finally focus on other people and things without them wishing step would return to team. I get they were close friends in the past but now itās time to focus on the future. I doubt HG is gonna stay quiet for long even with a slap on the wrist if u found his house
I think Ortega will stick around until we get rid of them for goodā¦
Not if they think step is a fake if they found out step is the new villain. It just depends on your actions to make it go that far.
Re-Gene copy my beloved. Its so heartbreaking but also so angsty and juicy. God, imagine what theyād do if they had a lovers relationship with step prior to that and/or believed the villain was sympathetic. Messed up does not even begin to cover it.
Then instead of persuading them to get back to the team, Ortega will disturb MC with attempts to āsaveā them from themselves 
I donāt believe Ortega will hold on to the idea that Sidestep is fake for too long. Theyāre not stupidā¦
Maybe it will take a while since step is the not the person they used to be. Ortega unfortunately doesnāt know about the farm and their relationship was built on a lie from the start so there trust issues as well. It was thanks to steps acting skills that hid their dual life until HG meeting.
Exactly. I love this ending as well as the one where you convince Ortega that it is actually you. Itās always so good (and heartbreaking) seeing them finally accepting that the one who did all of that is in fact Sidestep and not some re-gene copy.
I just donāt have it in me to try and convince Ortega, if thatās the conclusion they draw. My Sidestep in that situation justā¦ quietly accepts that everythingās broken, and starts to act the part.
Or thatās my recollection, anyway. Itās been a while.
I mean, I hope so. My sidestep canāt live without him 
I guess itās better to be cruel to be kind for a step like that. At least step doesnāt have to pretend to okay anymore.
Thatās actually one thing of my favourite endings where I let myself get caught on purpose unlike my usual paranoid step sweating from any mistakes that might happen.