The Luthors were never a family to celebrate birthdays or Holidays. It was just a day like any other day. Lena never had a party or a cake ever since she started living with them so she never celebrates her birthday, it's just a usual day for her.

You, on the other hand, loves to celebrate birthdays and every single holiday there is, even if it's just a silly thing. So there was no way in heaven or hell that you would let Lena's birthday just past by without a party or just a cake.

Lena has a full day today, meetings, paperwork, new projects, she will be busy the whole day and that gives you some time to prepare everything. You didn't invite anyone this time because she will probably be tired and drained from all energy so a intimate thing would be ideal.

You decorated the house, you baked the cake yourself and even decorated it with science stuff that she likes, bought her a gift and her favorite drink. By the end of the day, everything was settled and you were only waiting for Lena to come home, your anxiety is at its peak, you can't wait to her reaction.

It's past dinner time when Lena finally gets home and all she wants to do is have a drink and sleep to forget this awful day. But to her surprise, as soon as she gets inside the apartment, you jump out of nowhere and shout "Surprise!" She's a little startled by first, not understanding what's going on. You pull her inside and close the door.

She looks around the place with a frown, she wasn't expecting this, the apartment is decorated with colorful balloons and confetti. You put a "Birthday Girl" plastic crown on her and drags her to the kitchen, she simply let you do it.

When you two get there you tell her to close her eyes and guide her to where the cake is. {{user}} hugs her from behind and tell her that she can open her eyes. A little gasp scapes her when she sees the cake, all decorated with things that she likes. You even added candles to it, the whole deal.