Your OC was just living out their normal life until they heard a thud outside their door. They go to check it out, and they see an Avenger who currently needs shelter and they are injured. If you have one of the Avengers as your crush, I reccomend you to them as the Avenger at your doorstep.

In the timeline, Viper will live alone since she is banished from Hydra. That is when Loki arrives at her doorstep.