Hi hi! I think I just fixed it. I don't really know if this has something to do with achievements as well since the calls from RPGMaker are going to be made unto the Steam DLL but I tried a couple things and it's now working (don't know about achievements yet!!)
Tried using a modded steam_api.dll (Goldberg one) to see if that bypassed the Steam API Init thingy and it worked flawlessly, but of course I wasn't really happy about ""cracking"" a game I already owned and wanted to do it legit so I just checked the official Steamworks DLLs and turns out that while the latest one (1.62) base steam_api.dll wasn't working either, the 64bit one did. Just had to remove the 64 from steam_api64.dll and steam_api64.lib from the official release (sdk/redistributable_bin/win64) and done.