Love using my OP-1f to make these kinds of ambient sketches. Most of them sadly end up unfinished on my hard drive (or buried on an OP-1f tape), but I finally forced myself to arrange this one.
I used Ableton Live to record each part and add a few effects, mainly Ableton Echo, Valhalla VintageVerb, and Rymdigare by @humbletune for the weird noisy glitches (love this one!). All the sounds come from the OP-1f: Phase for the arpeggio, Dimension for the bass, and a few sample-based patches for the melody and high-pitched strings.
The rain was recorded separately with my Sony PCM-M10 and imported into Ableton as-is.
If I remember, the synths were from the internal synth engines with the exception of the voice-like pad sound which was from the sample folder (one of the stock samples).