(Haru)

Leads communicate through emails.
Lies are told about their lives for various reasons/insecurities.
They tackle other love interests in real life concurrently with their online relationship.
Haru's leads don't meet until the end, and while WL's leads have in person interactions throughout the series, they don't actually "meet" as their online counterparts until near end.

Leads communicate through online messages, don't meet in person until the end of the movies. Lies are told throughout both (catfishy).
I personally liked Haru much more than Contact. It gives a better sense of feelings and relationship than Contact does (IMO).

Two people become involved with each other through online messages/messaging. Main characters are navigating love, romance, relationships, break-ups, hook-ups...
When it rains, it pours drops the online chatting element very quickly, while in Haru its kept until the end. When it rains it pours also has a cheating element and moves much quicker, although, Haru also has some complicated relationships and touches on relationship troubles while the characters gradually discover their romantic connection.

Love Letter focuses on characters communicating with letters while Haru focuses on characters communicating through email.
Haru is set in city while Love Letter is set in the countryside.
Both movies are Japanese films and released at a similar time period.
Both films have that slow, but relaxing feeling to it.

Leads interact through messages (letters/emails) rather than meeting in person for the majority of these films. Female leads both navigate feelings for other in-person relationships while contacting male leads.