Jitsu wa...

Jitsu wa... ("I am...") is a Harem Genre manga which began in 2013. It has been published in English under the title My Monster Secret.

Our protagonist, Asahi Kuromine, is an Ordinary High School Student who harbors a crush on the beautiful and mysterious Youko Shiragami. While he's usually unable to keep a secret or hide his feelings, he's managed to keep this crush a secret for years, but when he finally manages to find the courage to ask her out, he accidentally learns that she's got a secret herself: she's a half-vampire. Her father only permits her to study at school so long as her secret remains secure, so Asahi vows to keep her true nature a secret...and she's not the only one at school who is more than she seems.

This manga got an anime adaptation in 2015.

Tropes used in Jitsu wa... include:

Accidental Pervert: Chapter 150. Kuromine accidentally grabs one of Mikan's breasts, trying to prevent her of hitting Okada's head again.
Brick Joke: Chapter 152. First Youko, then Akane decide the best way of imitating a mosquito is with a pencil on their mouth serving as a stand-in for the proboscis.
Cute Monster Girl: Youko is a very cute vampire girl.
Fan Disservice: Chapter 153. Genjirou wears an outfit that in a woman would be considered Stripperiffic. In his body, it's just horrifying.
Gender Bender: Shihou Shishido becomes a wolf-man (named Shirou).
Groin Attack: Chapter 151. Played for Laughs. Kuromine's groin is twisted thanks to the effects of Principal's time acceleration machine.
Kid From the Future: Rin is Mikan's granddaughter from the future.
Love Confession: In Chapter 150, Okada tells Kuromine he confessed, and was rejected by Mikan offscreen.
A Mind Is a Terrible Thing to Read: Okada can read minds. Sadly, that means things like reading the mind of his crush and discovering she likes another guy and will likely reject you.
Mobile Suit Human: Nagisa's race are humanoids not much larger than a human hand. To properly infiltrate mankind, they need one of these.
Our Werewolves Are Different: Shihou/Shirou transform when they see a picture of the full moon.
Paper-Thin Disguise: Chapter 152. Akane's costume of mosquito is only a hat, an abdomen prop, and a pencil meant to be the proboscis, and all of it barely hides her body.
Perpetual Frowner: Youko doesn't get to smile around most people, because she has to hide her fangs.
Prophetic Dreams: Subverted in Chapter 153. The Principal dreams about the return of her predecessor, that apparently didn't believe in the coexistence between humans non-humans. Turns out the person who The Principal thought it was her predecessor wasn't her at all.
Ripple Effect Indicator: Chapter 161. Future Nagisa herself. When the past one manifests her will to change the future in a way that is irreversible, the future one fades away.
Rule of Three: Chapter 152 features a caption describing in first place a mosquito order and sub-order, in second the fact only frmales suck blood, and in third it says it is Shiragami's rival.
Sizeshifter: Youko caughts Akane peeping on her and Asahi in Chapter 152, in miniature size, pretending to be a mosquito.
Surreal Humor: Chapter 151 runs on this, as Akane's clocks that accelerates time has the side effect of making things more "twisted".
Thanatos Gambit: Chapter 161. Turns out Future Nagisa was trying to force her past self to change, not caring if it would erase her.
Unwanted Harem: Asahi's pretty much only got eyes for Youko, though she's Oblivious to Love, which gives the other girls hope (and some of them would be okay with sharing anyway).