How to create Coarse-grained API from multiple microservice

I want to create a Coarse-grained API from multiple microservice APIs without using API Gateway can any one give an idea to achieve this.

Senario: I have different microservices for Notes and Diaries like Notes API, Docs API, Followups API, Reminders API. Each API is responsible for achieving the independent goals like creating a note, creating a document for the note and adding reminders for the note and setting the followups for the note independently.

I am able to achieve everything, but I have to create an API which should be able to handle above mentioned features for a Note.

We can achive this with API Management or Gateway, but I want to buld a service layer to achive this without using API Gateway.