Relax about what day it is with 安心

Kanji Explanation: Peace and ease with 安

After returning home from work, Nishikata is ready to sit back and relax for a bit. Takagi leans over and asks Nishikata if he knows what day it is.

西片(にしかた):: 「あれ？何(なん)の日(ひ)だっけ？」; “Huh? What day is it again?”
高木(たかぎ):: 「２人(ふたり)の記念日(きねんび)とかではないから安心(あんしん)して。」; “Relax, it's not an anniversary or anything like that.”; Literal: “Be at ease; it's not our anniversary or anything like that.”

Key Points

1安心(あんしん)して = “relax”

In this scene, 安心(あんしん)して reassures Nishikata that there is nothing dangerous behind the question.

2〜とかではない softens the statement

２人(ふたり)の記念日(きねんび)とかではない means “it’s not an anniversary or anything like that”.
とか presents 記念日(きねんび) as an example of the kind of “special day” Nishikata might be worrying about, which makes the reassurance sound lighter and more natural.

3２人(ふたり)の記念日(きねんび) = “an anniversary for the two of us”

２人(ふたり)の modifies 記念日(きねんび), so the phrase means a shared anniversary or relationship milestone.

4〜から安心(あんしん)して = reason + reassurance

The sentence is structured as [not an anniversary or anything like that] から [don’t worry].
Here から gives the reason for the reassurance: “Since it’s not that kind of day, you can relax.”