Alice wishes to send Bob a number $n$ between 0 and 255.
Bob has a private, public EC key pair $(b, B)$ where $B = bG$ and $G$ is an already agreed upon base point on the ed25519 curve.
Alice could roll a random number $r$ and perform a Diffie Hellman exchange to compute the shared secret $rB$. Alice could then use the shared secret $rB$ as a symmetric key to encrypt $n$, resulting in an encrypted payload $p$. Alice can then send Bob $R$ and $p$ where $R=rG$.
Bob would compute the shared secret as $bR$ and then use this as a symmetric key to decrypt the payload $p$ to discover $n$.
This requires Bob to perform some considerable computation, particularly the EC multiplication required to calculate $bR$.
What alternative method can Alice use to send $n$ to Bob, making use of Bob's EC key pair $(b, B)$, which would require the least taxing computation by Bob?
We are not too concerned with how taxing the computation is for Alice. It's only Bob's computation time that we wish to minimize.
Assume that observers of the communication are aware that some number $n$ between 0 and 255 is being transmitted. It is important that only Bob can discover Alice's choice of $n$, and important that an observer cannot detect when Alice sends the same value of $n$ to Bob twice. Observers are aware of Bob's public key $B$.
Given that many different people will want to send Bob a number $n$, it is perhaps likely that a good solution may involve Bob using a pre-computed lookup table of some sort.
The transmission to Bob cannot be interactive.