Ah choo! I'm so happy 

Want you, I only know you

It's you, you're so perfect

My heart is forever only looking at you

Anyone can see and be jealous

Our love is more precious than anything else

I want you to want me

Slowly, our love will quietly begin

Haseul featured this part in Everyday I Love You by ViVi. Note that the tone and meaning of this verse sounds similar to Heart Attack. 

Pounding more and more 

I'll give you all, take my heart

Surely you're my destiny

It shines fully in my heart

This must be what thrill feels like, darling

Eventually I fall into you

You attack my heart

Previously, getting Yves' attention became Chuu's main goal and in the end Haseul woke up the latter from her imagination (Heart Attack). 

Haseul (though indirectly) mentioned Chuu and their one-way acquaintance when with ViVi and the girls of LOOΠΔ 1/3 (Everyday I Love You). 

Ah choo! I'm so happy

I want you, I only know you

As Haseul's color is green, which is also the color of apple accompanying Chuu throughout her story. 

By the way, this is also a reference to another work by Rene Magritte (The Listening Room, 1952). 

Anyway, Haseul's appearance confirmed that the setting took place in London. Haseul dressed in blue and carrying Christmas presents was on her way to meet Heejin and Hyunjin. Even The Carol was distantly heard at the background when Chuu was found lying in the snow. 

Remember when I said ViViD was the gateway to enter LOOΠΔ 1/3 (light part) from the third unit (dark part) and vice versa? 

Also, remember when I said a second entry point was created by Haseul who cracked the mirror (Let Me In)?

It took me awhile to figure out how Haseul meeting Chuu became possible.

See the map below. Assume the X was the second entry point. 

Aside from being the capital of England, London is also where prime meridian is located.

A prime meridian is a meridian (line of longitude) in a geographical coordinate system at which longitude defined to be 0°. Together, a prime meridian and its antimeridian (the 180th meridian in 360°-system) form a great circle. 

Greenwich prime meridian in London was used as international standard until 1884. Today, the IERS Reference Meridian is widely used which deviates slightly from Greenwich.

As of 2017 the Greenwich meridian passes through both countries England and France. 

Meanwhile, the Paris meridian runs through the French Paris Observatory at longitude 2°20'14.03". It was a long-standing rival to Greenwich meridian as the prime meridian of the world.