The first volume of the Aves collection serves as an introduction to the specific aesthetic of the toy piano. It is musically notable for its simplicity and the intentional use of restricted pitch sets.
Maintain rhythmic precision despite the absence of traditional piano sustaining mechanisms.
Comparable difficulty and character — good candidates for what to learn next.
12 Preludes for Toy Piano - Aves 鳥 vol.I is rated Henle level 2 of 9 — beginner repertoire, roughly ABRSM grades 2–3.
You should be comfortable at Henle level 2 — meaning you can already play level 1–2 pieces cleanly. Learning it one level early is possible as a stretch piece, but more than that usually leads to months of frustration.
A typical performance of 12 Preludes for Toy Piano - Aves 鳥 vol.I lasts about 1 minute.
12 Preludes for Toy Piano - Aves 鳥 vol.I is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.
Pieces at a comparable difficulty and character include 12 Preludes for Toy Piano - Aves 鳥 vol.II by Kazue Rockzaemon Isida, 12 Preludes for Toy Piano or Celesta - Aves 鳥 vol.II by Kazue Rockzaemon Isida, 12 Preludes for Toy Piano - Aves 鳥 by Kazue Rockzaemon Isida — see the full similar-pieces list on this page.