4 Years Later after writting this and i'm back to make a few changes, around 90% of the Any% route has been the same since 2016, but some small improvements just happened recently, so i'm here to keep everything clean. This guide made by text contains some easy steps to teach you how to finish the game with the fastest route, and to start off, let me explain how the game works, so you can understand why this is the fastest route:

[EXPLAINING THE GAME]

This game is based on choices, that are made by triggering inklings (random events through the World Map), each choice will provide you a different path, with a different faction. I believe that the maximum inklings you can trigger in one play is about 25~30 (in case your going for the true ending or something like that). However, since most of the first available inklings doesn't affect your possible endings, turns out that the game can be finished by triggering only 10 inklings (only 3 of them are important to get to the fastest ending, all the other 7 inklings are purely random and they need to be triggered because, somehow, the game will only unlock the story inklings if you play through a certain amount of random inklings first.

[HOW TO GET THE FASTEST ENDING]

I already played and ran this game multiple times on my X360, and i figured out this ending by watching the actual PC Version WR held by 'therealbmanbeast' and this route can be done in any category including 'Instant Kill' (as long as you have a good enemy RNG) and it goes like this:

1. (SKIP CUTSCENE x2) choose any dialogue to get warped to Takatane Village (SKIP CUTSCENE x2);
2. Kick the wooden door in front of you and get out of Osei's House (SKIP CUTSCENE);
3. Make your way down the stairs and go talk to Kota (SKIP CUTSCENE) and choose ''Calm Down, Kid'' dialogue (SKIP CUTSCENE x2);
4. Open the Menu > Map > World Map, warp to Omiki Town;
5. Jump over the fence and run towards the bridge to trigger the inkling (SKIP CUTSCENE);
6. Warp to Castle Amana;
7. Talk to the guard in front of the main gate and choose ''Yes!, I have skills to prove!'' (SKIP CUTSCENE);
8. Defeat all enemies as fast as you can (SKIP CUTSCENE);
9. Warp to Road;
10. Run through the trees in the right and go towards the temple entrance (SKIP CUTSCENE);
11. Warp to Castle Minori;
12. Talk to the guard at the gate and choose ''Why don't you use me?'';
13. Deal enough damage to any guard until the cutscene starts (about 40~50% of damage) (SKIP CUTSCENE x2);
14. Warp to Kuchihagahara;
15. Go to Shinnosuke's House (SKIP CUTSCENE);
16. Warp to Posting Station, then turn back and warp to Takatane Village;
17. Go upstairs to Osei's House and approach Munechika (SKIP CUTSCENE) then choose ''Are you harassing me?!'' (this inkling will skip one of Shinnosuke's last Inklings, saving about 30~35 seconds of walking and skipping things);
18. Go home and sleep until NIGHT;
19. Warp to Castle Minori (SKIP CUTSCENE x4) (this auto-inkling will skip one of Shinnosuke's Inklings, saving about 40~50 seconds of walking and skipping things);
20. Warp to Kuchihagahara;
21. Talk to Shinnosuke and choose ''Sakura... Sakurai?'' dialogue;
22. Warp to Posting Station, then turn back and warp to Takatane Village;
23. Go home and sleep until MORNING;
24. Go talk to Kota, choose ''You're pretty good'' (SKIP CUTSCENE);
25. Warp to Castle Amana;
26. Go to the main building entrance (SKIP CUTSCENE) choose ''The Crest is in Takatane Village'' (SKIP CUTSCENE);
27. The game will auto-warp you to the Village (SKIP CUTSCENE x4);
28. Warp to Kuchihagahara (SKIP CUTSCENE x4).

I'm currently planning on Speedrunning this game again, now on PC version, so if there is anything relevant to update here, i'll be doing so.