I've been trying to translate this set, but the grammar simply eludes me on this one. It might require some inside knowledge of the fanfic on which the illustrations are based.

「奉太郎29歳誕生日の絵の女の子をちゃんと描きたいなと思って描いてみました。」

奉太郎 - Houtarou
29歳誕生日[の] - [of the] 29th birthday
絵[の] - [of the] picture (illustration, not photograph)
女の子[を] - girl
ちゃんと描きたいなと思って描いてみました。- I wanted to draw it, so I did.

Depending on the context, the meaning could be one of several things. If a native speaker could chime in, that'd be great.

1. "I wanted to draw the girl from the picture of (illustrating the event of) Houtarou's 29th birthday, so I did." (I don't know what picture this refers to.)
2. "I wanted to draw the girl in the picture for (on the occasion of) Houtarou's 29th birthday, so I did." (Would require the artist to be in character. Also dicey grammar.)
3. "I wanted to draw the girl from the picture from (which was published on) Houtarou's 29th birthday, so I did." (Seems unlikely in context, but feels grammatically okay.)
4. "I wanted to draw the girl in the picture on (as she appeared at) Houtarou's 29th birthday, so I did." (Makes decent sense, but dicey grammar.)
5. "I wanted to draw the picture girl (defining her by the paper she's holding?) at Houtarou's 29th birthday, so I did." (Grammatically very fluid, but makes the least sense to me.)